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FAQs on Biological Pond Filtration

Related Articles: Filtering Ponds Biologically, Pond Filtration, Up-flow Filtration, In-Pond Filtration, Ultraviolet Filtration for Ponds, Pond Filter Media

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Good quality "filter bags" with ties to return lines are excellent for catching the majority of solids for expedient removal. The best, bar none, are Emperor Aquatics, shown here.

Aquatic Gardens

Ponds, Streams, Waterfalls & Fountains:
Volume 1. Design & Construction
Volume 2. Maintenance, Stocking, Examples

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by Robert (Bob) Fenner

Is this gph rate enough? Fancy goldfish in a small pond      3/3/17
Hi. I couldn’t find the information that could help me on your site. I need to know the gph and filtration requirements of one adult fancy goldfish. I have a 40 gallon oval pond. It's made of Ldpe Plastic. I checked to be sure it was safe to use. It measures 27" W x 40" L x 13" Height. I got a Tetra submersible flat box filter good for 200 to 2,000 gallons for it. I got a Superflo 1300 pump for it. It has a gph rate of 306 gph. I think I got enough power to run the filter. But I got 1 burning question for you. Is my pump’s 306 gph enough for 1 fancy goldfish in this pond? Thank you.
<It is more than adequate; in fact, do see that this current isn't buffeting the goldfish about... it may have to be restricted... best on the discharge side; with a variable valve. Bob Fenner
UV and Liner Questions       3/4/17

Hello Bob. Thank you for answering my previous question.
<Welcome Cam>
I have a few more questions. I have a 40 gallon oval pond. It's made of Ldpe Plastic. I checked to be sure it was safe to use. It measures 27" W x 40" L x 13" Height. I got a Tetra submersible flat box filter good for 200 to 2,000 gallons for it. I got a Superflow 1300 pump for it. It has a gph rate of 306 gph. Is the gph enough to add on a UV sterilizer as well?
<Indeed it is; yes>
If so, what is the type and gph rating of the UV should I get?
<If there is an easy way to attach the filter pump to the UV, I would use it for this as well; for both the filter and UV>
And my second question. Should I use a liner with this pond?
<No liner is necessary. I would just use it as is>
Thank you.
<Welcome. Bob Fenner>
2nd Goldfish GPH Question... Repeats       3/7/17

Hello again. Here is a repeat on the specifications on my pond. I have a 40 gallon oval pond. It's made of Ldpe Plastic. It measures 27" W x 40" L x 13" Height. I got a uv filter fountain hybrid with A 265 gph. The uv has a
13 watt bulb.
My question is, will the 265 gph be too much for 1 fancy goldfish?
<Already asked and responded to...>

I will only get common fantails, Ryukins, Orandas, or Ranchus. This will be an outdoor pond. I live in the subtropical AZ desert. Ice never makes the water freeze over. So that wouldn't be a problem. I got 2 fake pond lotus I plan to use as shade for the fish. They are both 6 inches in diameter. I have the option of adding two more if I need to. I don't want snails and have no luck with live plants. So my only option for algae control is algaecide. I am very careful with algaecide. Is there anything else you think I should do in the planning of my pond? Thank you.
<Am not a fan of pond algicides... too dangerous, toxic... at any concentration. READ please where you were referred to (again). B>
RE: 2nd Goldfish GPH Question      3/7/17

Ok. Thank you Bob. Just making sure I am correct by asking you first. You know a lot more than me.
<Am much older; studied in the field Cam. B>

Filter photo     3/8/17
Here is a photo of the filter I will be using in my 40 gallon pond.
<? This looks to be just a fountain spray pump with a screen. NOT a filter; NOT what you mentioned: "Tetra submersible flat box filter good for 200 to 2,000 gallons for it. I got a Superflow 1300 pump for it. It has a gph rate of 306 gph">
Here is a picture of Leia, my green Ranchu. ��
<Very nice. B>

Re: Filter photo       3/8/17
Thank you Bob. ��Yeah, the filter is a new one I am going to be trying. They tell me it filters and reviews say it keeps the pond clean. It has a gph of 265 and is recommended for ponds up to 500 gallons. It also has a uv and a fountain. They said it was designed for small ponds. I did what research I could on it. It seems to filter ok.
<READ on WWM re pond filtration.>
RE: Filter photo       3/8/17

Ok. Got another filter. What do you think of this one?
<How is biological filtration provided? SEE as in READ on WWM Re.>
Pennington Aquagarden In pond 5 in 1 300
3 stage filtration
203 gph pump
20 watt uv clarifier
Has a fountain feature
Dimensions 14” W x 15” D x 7” H
Water flow is adjustable

RE: Filter photo       3/9/17
How is biological filtration provided? Well, it has course foam pad, a medium foam pad, a polymer wool pad, and ceramic biomedia. Water flows through the top of the filter, through the foams, then through the ceramic media to the UV. Then it goes from there to exit through the pump. Does this answer your question? Anything wrong with this?
<It does sound like the stmt.: Triple filtration provided. This should work. I would move a good deal of your established ponds water to the new pond to prime the bio. B>

RE: Filter photo          3/10/17
Can do! Here is some drawings I did of what the setup might look like when completed.
Thank you so much Bob. Your help means a lot to me. I greatly appreciate it.
<Ahh; very nice. Thank you for sharing>
RE: Filter photo          3/10/17

You are welcome

Advice about pond pump & filter, and Pb    1/10/11
I am replacing a pond pump (1/6hp Seahorse by Pentair 3250 gph) with a more powerful and efficient pump (Sequence 5000 gph).
<Very good sub., move>
I'm also replacing the filter.
The new pump will attach to 2" PVC and feed an upflow filter I am making from a 100 gallon plastic stock tank (the kind they use to water cattle and horses, etc).
<Understood... IF possible, I'd choose a much larger one/volume. This pump, if all water is directed through the planned one, will be too much flow>
The drain will be on the side on the top.
What size drain pipe do I need at the top of the tub, considering that the exit will be gravity fed?
<... Mmm, likely two 4 inchers... Really, redundancy is a good idea here.
Please read:
and http://wetwebmedia.com/PondSubWebIndex/upflowfiltpds.htm
and the linked files above. Bob Fenner>
Thank you.

Nitrogen Cycle Stuck in Neutral   9/24/10
Dear Bob,
<Hello Allen>
I've written before about this subject. I have a new concrete Koi pond (1,200 gallons), epoxy painted. I have a 2,300 GPH Seahorse pump pumping from a skimmer and bottom drain into a Laguna filter/waterfall return. I have 6 small Koi.
<I see>
The Ammonia spiked as expected, maybe even a little earlier than expected given the small fish load and light feedings, but it spiked and then went to zero as expected. Along with the Ammonia going down, the Nitrites went up: To 1.0 (Purple - using an API test-tube test kit) where they remained for 3 weeks. I used 2 lbs salt per 100 gallons to prevent brown blood disease, the fish are active, eating and seemingly happy.
5 weeks ago the purple (1.0) Nitrites became BLUE (.25 to .50 on the API card) where they have remained for the last 5 weeks. No Change at all.
Every 3rd time I test, I test the tap water as a control and it is truly 0 (turquoise) and I ALSO test the Nitrates and they remain 0 as well <Mmm, "something" is "using them up"... Likely simple photosynthates... perhaps algae>
The pH is 8.2
the kH is 130+
The UV Sterilizer is off
I've used 2,400 gallons "worth" of Superbugs
<Oh, or these>
I've used 1,800 gallons "worth" of a product called "NIte-Out II" from Microbe-lift
<And this could have a discernible effect as well>
and the Nitrite test remains dark blue.
At night, when it's quiet, I think I hear the Nitrites laughing at me.
Is it possible that I have a substance in the system that kills those bacteria?
<Mmm, perhaps...>
What am I doing wrong?
<Likely not much to nothing. I would continue to feed sparingly, and do w/o adding any more bacteria or supplements. Time will solve this issue I assure you. Cheers, Bob Fenner>
Nitrogen cycle stuck in neutral? Re-send   9/25/10
Dear Bob,
<Just yesterday... for which I responded...>
I've written before about this subject. I have a new concrete Koi pond (1,200 gallons), epoxy painted. I have a 2,300 GPH Seahorse pump pumping from a skimmer and bottom drain into a Laguna filter/waterfall return. I have 6 small Koi.
The Ammonia spiked as expected, maybe even a little earlier than expected given the small fish load and light feedings, but it spiked and then went to zero as expected. Along with the Ammonia going down, the
Nitrites went up: To 1.0 (Purple - using an API test-tube test kit) where they remained for 3 weeks. I used 2 lbs salt per 100 gallons to prevent brown blood disease, the fish are active, eating and seemingly
5 weeks ago the purple (1.0) Nitrites became BLUE (.25 to .50 on the API card) where they have remained for the last 5 weeks.
No Change at all.
Every 3rd time I test, I test the tap water as a control and it is truly 0 (turquoise) and I ALSO test the Nitrates and they remain 0 as well
The pH is 8.2
the kH is 130+
The UV Sterilizer is off
I've used 2,400 gallons "worth" of Superbugs
I've used 1,800 gallons "worth" of a product called "NIte-Out II" from Microbe-lift
and the Nitrite test remains dark blue.
At night, when it's quiet, I think I hear the Nitrites laughing at me.
What am I doing wrong?
<The same response... see WWM's Dailies or if later than today, look at cycling pond systems. BobF>

Balancing objectives, bio-cycling new pond  7/28/10
Dear Crew,
We have set up a new 1,300 gallon pond. We treated the water with Amquel initially
<Mmm, better by far to "just wait"... let a week go by... to liberate sanitizer (Chloramine)>
and then aged it for 4 weeks
<Oh! So Amquel was unnecessary>
with filter and aeration. Finally we added a product our local Koi store sells called "super bugs"
<What is this specifically? A culture of nitrifying bacteria?>
and then 3 days later added 5 fingerling Koi. The nitrogen cycle started as predicted with the Ammonia slowly climbing up to .25
<... toxic, debilitating>
and then slowly back down. Along the way we sometimes gave way to worry about stress and added tiny amounts of Amquel. We knew this would affect the cycle by binding the ammonia that the bacteria needed, but we did it sparingly hoping that the bacteria would simply take longer to cycle.
<A reasonable assumption>
Now, the ammonia is zero, but the nitrites are over .50
<Also toxic...>
and maybe even climbing. The fish are flashing occasionally and certainly in distress.
<I'd remove them to elsewhere till this system is completely cycled>
Everything I've read says to do a minimum 25% water change, but since we don't have a place to fill and treat 325 gallons of water, we'll need to pour our local chloramine-treated water into the pond while interspersing
<... or just wait, feed the system a bit of food/s to finish cycling>
My concern is that I'll be changing too many things too quickly and substituting one terribly toxic condition for another while subjecting the fish to toxic conditions AND sudden change.
How do I get out of this cycle?
Thank you,
<Read here: http://wetwebmedia.com/FWSubWebIndex/fwestcycling.htm
and as much of the linked files above as you deem gains you a sufficient understanding of your present position, options. At any length, if you don't move the tategoi, I'd stop feeding period... but the best course of action is to remove them to an established system, wait the few weeks till there is no NO2, some accumulating NO3, evidence of complete cycling here.
Bob Fenner>

biofilter for Koi pond 7/2/09
Hello, I was wondering if you have any advice on building a bio filter for my Koi pond. My pond is 60,000 gallons (its about 40x30 and 8ft deep)
<Ahh, good size>
and it has a ledge on the inside all the way around that i use to put my potted plants on. I have done a lot of looking online but all the filters i find are for smaller ponds any help will be greatly appreciated!! Thanks
<There are a few approaches one can take here... a good question to reply with is "what do you hope to accomplish" with this system, the filtration?
IF only to make the water viable (though not optimized for health and viewing), a much more simple, more passive "rock" emplacement can be devised... IF more clarity is an issue, plants can be added, and/or a
working UV and pump system... At any length, a cursory review of all can be read here:
scroll down to the fourth tray... and read.
Bob Fenner>

Water feature advice  6/10/07 Hello crew! After coming across your site I have become an avid reader of your advice to queries raised by other users and on Bob Fenner's articles. I am an Englishman living in Mallorca (a small island in the Med approximately 150 miles East of Barcelona). I have a brand new water  feature >in my garden, which as a result of a neighbour's wall collapsing and having had to be rebuilt as an integral part of the structural retaining solution, is now considerably larger than was ever originally envisaged or intended. >This was intended to be an ornamental fountain that predominantly was for creating the sound of falling water whilst also being aesthetically pleasing. >In its revised much larger incarnation the opportunity has arisen to also use this feature to keep freshwater fish and in the process of researching these options I came across your site. >Whilst a little unusual relative to most questions raised on your site I still hope that you may be able to help to me as I do not so much have many specific >questions rather more a desire for your professional overview on certain issues that will help me keep fish. <Okay> >Having read many of Bob Fenner's articles about pond design it is clear to me that I will have to try and make the best of a bad lot as many things could have been done differently if this had been intended as an  aquarium from the outset. <A common resound...> >I enclose some photos in jpeg format in 72 dpi to provide an overview of this feature. <Didn't make it...> >The technical specifications are as follows: >The pond at the bottom of the waterfall holds approximately 170 us gallons and so is I hope large enough to not encounter the instability problems encountered by ponds less than 100 gallons. (with hindsight would have made it bigger) <Yes> >The dimensions approximately are: (Dimensions of the body of water - the structure itself is larger) >Length 1.28 m (4.2 ft) >Width 0.75 m (2.46 ft) >Depth 0.68 m (2.23 ft) >The fountain has a fall of 1m (approx 3ft) and the water is pumped from the reservoir (pond) at the base in to a bowl (see photo) and this in turn spills over and falls in to the reservoir. <Even discounting wind... there will be some splash, spray here. A trip/fall hazard> >The pump (I now know unfortunately) is the submerged type, and shifts 1.5 litres per 15 seconds and so re-circulates the whole reservoir every two hours. Due to the first bowl which creates a mini waterfall and then the main waterfall with its 1m drop I think the water is well aerated. >The pump is not located on the bottom but half way down the reservoir on a stone shelf, the pond itself is lined with stone and concrete. So hopefully there will be no problems pumping stale foul water off the bottom of the pond. What I would like your expert opinion on is of all the filtration mechanisms available WHICH would you implement to filter this pond if it were yours? <Is this to be a biological system?> >It has taken a long time to get to this stage so I really don't want to implement a solution that will entail reconstructing the fountain again unless absolutely essential! Having read a lot on your site I was wondering whether I could create a sort of filter in the fountain bowl if I half filled it with two different grades of pebbles with some fine stainless steel mesh between the layers?) <Will serve as something of an intake strainer only... useful for keeping material out of the pump mechanism> Obviously back washing would be impossible and this would have to be done manually. <Yes...> >I would also be interested in your opinion of what my fish options are - our climate is a hot summer up to a maximum of 110F but probably averaging mid 90's(f) in summer with a mild winter never below circa 41f coldest and usually warmer. Also how many fish would be sensible for maintaining this as a balanced pond <... Trouble in this small volume... Are you adverse to "switching out" the livestock for cooler/hotter seasons?> >I do however want the water to remain crystal clear <Oh! You will need to do a bit of retrofitting then... likely remoting physical filtration (UV, or perhaps a purposeful ozonizer), along with biological filtration, likely mechanical...> and intend to put water plants into the pond in accordance with the recommendations on your site. Any advice or plant recommendations very welcome) <Do take a look/see re what you have available there... No sense making a "wish list" for species you can't get your hands on> >I have also taken on board the comments about changing water frequently. It is too late to put in a sump drain but I was wondering if I bought a separate electric hand pump if I could pump foul water off the bottom straight out of the pond and then refill it? <Good idea... likely can pump the water regularly onto surrounding landscape...> >On other sites I have also seen pond vacuum cleaners advertised for cleaning the bottom surfaces - in your experience (if any) are these any good? <Most are marginally functional> >The pond will not suffer from surface water run off as it is effectively isolated and can be filled by tap or well water. >Any comments you may have would be very useful but from what I have read the biggest obstacle to which I require the most effective retrospective solution, is the filtration question. >Hoping that you can help, >Yours sincerely >TCH <Please, in future, send mail sans carats/hard returns. Bob Fenner>

Fishy <I'll say!>... Over bio-loaded pond... stop-gap measures   4/19/07 Dear Bob & crew <Big D> Last night, for no apparent reason, my white tip reef shark bit the fluke of my bottlenose dolphin I bet you wish you had a nickel from every time you've heard THAT, right? (ahem - just kidding) <Heeeee!> Finally, my son's marine aquarium is stable, thanks in great part to your wonderful site and expert advice. Things are nice and quiet. Yep.  You guessed it. Too quiet. Nature abhors me having a nice, relaxing day. <And a vacuum!> So a woman I know called and told me she just bought a house with a Koi pond and asked if I could come take a look.   So I get there and it's a nice house and a nice pond.   There are six 22+ inch Koi and two 8 inch Koi in a 650 gallon pond with a 800 GPH submersible pump emptying into a 30 gallon filter. <Yikes... too much life, too little water, filter...>   OK, it was a nice pond when there were 8 fingerlings in it.   So I whip out my test kit and get exactly what I expected:  1.0+ Ammonia, 5.0 Nitrite & 8.1 PH.    So I ask her:  Are you sure they're not dead and it's just the current blowing them around? <Good one> Well, no I didn't ask exactly that ...  but now I'm under more stress than the Koi. Changing close to 650 gallons of water over 36 hours improved things dramatically, but I swear, even as I'm doing this ... a couple of the Koi would nose to me, head almost out of water and then turn and shoot poop out as if to say "we've evolved, we LIKE ammonia!" <Doubtful> Anyway ... a bigger pond and less fish is the answer and we're working the logistics on that ... but in the near term, what would you think about 4 litres each of Purigen and Phos-Guard in the filter as an artificial assistant while I dig the other hole, pour the other cement and beg the homeowner for the funds to do all this? <This and more or less constant water changing, very limited feeding... Bob Fenner> Pond Filtration  12/13/05 Robert, <Sorry for the late reply... have been away> I read several of you online articles regarding pond filtration (etc.). I'm glad you are lending a helping had to the many pond keepers who suffer the ubiquitous "pea soup" syndrome. <Glad to share> I'll come quickly to my point. In the articles I wrote for FAMA, I outlined a very simple and natural method for keeping virtually any pond crystal clear and 'algae free'. Since 1996, I have built ponds in Tallahassee FL and at my current residence in Kaneohe Hawaii. (some Florida pictures here: http://www.davehanby.com/dsh_old/tallahassee_treefort_page.htm). Despite going from 'sunny' to 'sunnier', each pond that I constructed has always had crystal clear water with no algae problem what-so-ever. <Impressive!> The only mechanical device that I have ever used is a water pump which moves the water from the pond up to a 'swamp filter'. The pond at my current residence is shallow, has no shade and receives year-round direct tropical sunlight.  The pond is fully stocked with several dozen carp species as well as an abundance of guppies and toad tadpoles. Despite these difficult conditions, the pond has always been crystal clear. I had the same results in Florida and in Connecticut. Each time, the method of success was simply a 'swamp filter' equal in size to the display pond. <These do work> In that I imagine that you are a pond keeper, I invite you to try a swamp filter and see how it works for you. <Have used and built many of these over the years> The simple guidelines are to dig a 'second pond' on level or above your display pond. Once dug and lined, connect the two with a spillway to make sure the water flows correctly. I use a 40 watt 'pond' pump <Wow, low electrical consumption> on my current system but have used all manner of pumps, powerheads and sump-pumps in the past. Once the water level has been established, turn off the pump and put the excavated dirt back in the new pond (if you soil is predominantly clay, you might use sand for the top 6'). The water level in the 'swamp' should be about 1' across the entire surface. You can plant the swamp with any water plant (which may quickly outgrow the space). Wait a few days for things to settle and then start the pump (which should be run 24/7 from that point on). It will take a few weeks for the water to 'settle' (muddy until then). After two - three months, you should have perfectly clear water and no more algae problems. I hope you may have success with this method. Aloha, David Hanby <Thank you for your input David. You might want to re-sell your pond articles to our on-line zine... Bob Fenner> Pond biofilters  9/8/05 Hello Bob, Am interested in building a bio filter per your spec.s as shown on website. Question - what is down side when electrical outage stops pump? Does not the 'bad bacteria' enter the fish pond when the power comes back on? Thanks in advance Frank P.    <Can indeed be trouble... if much "gunk" is accumulated, goes anaerobic... regular backwashing, and discharging water over a falls or stream generally discounts any such possible disadvantage... though one could leave out a back-check valve or arrange a perpetual siphon... to drain the filter basin in the event of such a pump/ing failure. Bob Fenner> DIY pond filter 8/28/05 Hi, I am very new to pond and Koi keeping. I have been doing some research on building my own filter system. Currently I have a very small pond 260 gallons and heavy stocked. I am currently using the Tetra PF3 which I thought was well large enough. I found out that I am running the water through it too fast and causing my Ph to be low and the nitrate to be high. <Ahh, common... good that you have discovered this... in such a small volume, highly stocked... can be real trouble if maintenance lapses> I have turned  back the water flow as of today and I'll see if this helps. I do have interest in the 60 gallon drum. I would like to know what pump and size that you recommend. <There are "rules of thumb" re the amount of actual flow per square foot, cubic foot of filter media... best to get a bit too-large pump, divert excess flow around the filter (not through)... save up for your new pond...> Good news... I am going to enlarge my pond this winter to about 1200 gallons   If I could go bigger I would, I have limited space and I am using every square inch that I can find. <Still... a near five time increase in volume!> Only if I had more room. The new pond is going to be in the corner of the patio in a somewhat L curve shape, it will be about 48" tall and I am going to make it like a bar that you can sit and watch the beautiful Koi while eating, etc. <Very nice> I can use all the information that you can give me and I thank you for the information that I have already gotten. Thanks again, Bobbie <Please take a (re)read through our Pond Subweb: http://www.wetwebmedia.com/PondSubWebIndex/Pond%20Sub%20Web.htm The articles and FAQs files on construction, filtration... and maintenance will help you guide yourself.  

Biological Pond Filtration 7/10/05 Hey Bob!  I hope you are enjoying your summer so far!  I just wanted to say thank you so much for your suggestions and ideas on my new pond construction over the past few weeks. <Welcome> I know you look at HUNDREDS of emails a week so probably don't remember the specifics, but suffice it to say that I have taken all of your suggestions and worked them into the plans for the pond and it is dug now (BY HAND!  I'm Tired!) <I'll bet!> Anyway, the original pond was going to be 4' wide by 8' long and sloping from 4' - 1.5' deep with 2 big barrel filters. After re-reading your article/FAQ's about the filtration, I have decided to scrap the barrel filters and go with a separate/attached open gravel filter (reverse flow) like you had suggested in the article. <Ahh! Much better> The pond is now 8' long X 6' wide X 4' deep all around with a shelf of approx 20" around the front and 1 side for planting pots.  (Approximately 1200 GAL plus whatever is in the filter compartment) The filter is 2' long X 6' wide X 27 1/2" deep with the return water fall across the entire 6' span approximately 5" drop to the pond. If you have a minute, could you see the attached link for the picture of the filter and tell me what you think? http://i5.photobucket.com/albums/y195/navajo001/gravelfilter1.jpg <Mmm, you might want to look into something a bit stronger, more permanent for media support in the filter... the egg-crate won't last... may break from the get-go... and a mechanism for rinsing, washing under the substrate (space) will really extend the period of time between cleanings... can be "rinse pipes" extending from up above... and I suspect that you have valving on the pump... I would insert a couple of true unions, a check valve...> Since I cannot find any stainless steel screen wire locally and ordering it is very expensive, I decided to go with 3 layers of egg crate/light diffuser.  I think that as long as there is no more than 8" between any of the supporting bricks, it will hold. <We'll see> Also, I am assuming that using the bricks with the 3 big holes in them (standing edgewise) will promote better water flow. <Yes> As far as cleaning, will a garden hose be enough or will the pressure washer be even better? <The latter... a few methods can be employed... the simplest is to build a sort of nozzle on the end of a length of PVC pipe... with a ninety/elbow... and a hose-pipe connector on the other end to connect to your garden hose... and stick this down, through large (ABS, irrigation pipe...) down through the substrate, rinse about in the area of the brick/block supports, while the filter is being drained> The main focus of this rebuild is ease of maintenance for the wife, and better living conditions for the 4 Koi. <I understand> One last question if you don't mind.  Since we live in the mountains of Northern VA, it does get down around 0 Deg F a couple times in the winter, but only for short times and is usually closer to the teens/twenty's during the winter.  With the addition of the 3.5" thick Styrofoam sheets that are going between the walls of the raised portion and the flow from the Sequence 750 pump (~ 3000 GPH) do you think that leaving the filter/pump running during the winter will keep the pond from freezing, or should we just continue to shut everything down when the temp drops below ~ 40 DEG F or so? <Mmm, hard to say definitively... IF you're very sure that there will not be persistent, long sub-freezing temp.s...> As always, your time/experience is much appreciated!  Take care and have a wonderful summer! Tom (The Tool Man) <Am doing so... though am sore as well... from digging in my rodent farm... Uhh, garden. Bob Fenner>

Re: Biological Pond Filtration 7/11/05 Hey Bob! <Tom> Thank you so much for taking the time to answer my NUMEROUS questions!  I know you have better things to do.  I just want to get it right.  REALLY don't want to have to do it again. <I really do understand this... most folks (if they stay in the hobby/interest, IF) end up doing extensive and expensive re-do's here> OK, thank you for the polite "smack up-side the head"!  As much time, effort, and money as I'm putting into this, it would be silly to try to cut corners at this late stage.  I have ordered the stainless mesh wire (1/2" Mesh Welded Stainless .063" Wire Dia.) to use in lieu of the egg crate. <A wise choice, investment> Also, yes, I have a check valve and true unions for the pump.  I neglected to put them in the diagram.  Sorry. <No worries. Just checking> As far as the back washing goes, I have updated my picture with your recommendations.  Could you please take a look and let me know if I have it right? http://i5.photobucket.com/albums/y195/navajo001/gravelfilter1.jpg <Ahh, very nice> If I understand you right, I would burry a couple of pipes (3" dia?) with holes in the sides and bottom and run a hose adapted piece of pipe down with a 90 deg bend in the end inside for back washing the screen and lower portion of the gravel during draining. <Two inch will/would likely do here... and just for mentioning it, you can even rig up a fitting for pressurized air... to help jostle, lift, clean all...> I got all the post holes dug and poured with concrete this weekend.  24 Holes 2' deep mixed about 1500 lbs of concrete in a 5 gallon bucket with a stick!  NOT something I want to do again!  ;-) <Uggh! Will share with you a recent addition on one of our rental homes decks... some seven yards... yes, at two and a half tons per yard... concrete, to make a base for a couple tons more flagstone... Wife asks "why did you hire a pumper? You could have wheel barrowed the concrete in"... that's uh, 35,000 pounds... even if I could move a hundred pounds at a go, that would be 350 trips... with the concrete truck stand around time at some $150 per hour... and my back!> Thank you so much for your time and willingness to share! Take care! <Glad to help. Bob Fenner>

Freshwater Protein Skimming (ponds) 7/9/05 Bob, <Joe> Crazy guy here. <Mmm, not so crazy... You have good ideas, well-worded questions...> Of late, a variety of places on the web have begun selling freshwater protein skimmers for ponds. From reading on various web boards, it would appear that these don't work very well. <Correct... physical properties of water, undesirable molecules> It seems that if the pond is quite dirty, the skimmer pulls out maybe a cup of skimmate, and then sort of shuts down. The few that do use them, seem to use them once in a while, on timers and the like. Is this your impression of the reality of freshwater protein skimming today? <Yes> Pursuant to that: If you were going to conduct a scientifically controlled experiment in protein skimming in a 45 gallon freshwater source, what would you put in the freshwater that one could exactly repeat time and time again for each experiment? <Likely a "protein mix" like those made for human consumption...> I've thought of a whey concentrate (almost pure protein), but don't have any idea if that would be a good test... Know of anything that would be representative, and is fairly cheap? We should hang out and get a beer some time soon, <Now other ideas are coming to mind... Bob Fenner> Joe Kraska Construction of Biological Filters for Ponds Do you have any specific instructions or diagrams on how to construct a biological filter for a pond?  Do you construct biological filters? <No longer construct anything. What we have re is posted on WWM. Bob Fenner>

Duck Pond Hello I didn't find anything related to this question. I have a duck / goose pond approximately 2000 gallons, I have two filters hooked up one a regular sand filter for an in ground swimming pool ( I filled it with pea gravel ) and connected to this is a modern media filter ( in ground pool also ). I can't and really want to figure out a way to keep it relatively clean. I have not used or know of any chemicals available for use and or and other grander filter system. I do have a small zoo and good looking enclosures is a must for me. There are no fish in the pond and it house about 20 different ducks. I have the filters set up as a waterfall at the export side of the filters. THANKS BOB PILZ <There are actual "formulae" for figuring how many water fowl one can/should have per acres and acre-feet of ponds, lakes... a two k gallon system is just going to be a real mess, no matter how much filtration you can affix to it. I encourage you (if at all possible) to instead devise a system of flushing the basin with new water, either continuously or in a pulsed fashion... draining it from a/the bottom... about all the volume... daily. Bob Fenner, who knows what a stinky mess these birds make>

Koi pond no filter? Bob hello. Just found your site recently and I'm glad I did. I have an established cement and sealed (6 yr.) Outdoor N. California Koi pond (9 Koi all about 13-18") approx. 2500 gallons, waterfall, 3' to 18" deep with gravel bottom and a planted island with hyacinth lilies etc. I am running a large pool sand filter with pea gravel for biological on a timer for 9 hours a day <Yikes.... can be trouble during warmer weather, accumulated gunk... with leaving this media w/o circulation...> and a Hayward paper filter for mechanical which I run about a week on and a week off just to clear the water when needed. No UV. The pool/pea filter is finally getting clogged a bit and I have to backwash it more frequently than I'd like. <Yes... Very common... as am sure you know now> My question is can I get rid of the pool filter completely now that everything is established and just run through the paper filter when needed? <Mmm, no... will clog VERY frequently... quite frustrating... switching out cartridges, paying high electrical bills for diminished flows...> I don't think the bio filter is doing much anyway as it is on only 9 hours a day and the pond with rock/plants is probably now the real bio filter. <Could be> Just as my reef tank no longer uses bio balls and relies on the live rock for bio filtration. The pond is clear and the Koi are all healthy and happy. Thoughts? Thanks Gregg <For the size system, number/biomass of fish... you may "get away" with what you propose, but I strongly encourage you to think about all this a bit more... and to resolve to at least "just" switch out the pea gravel (yes, a job) from the pool filter (for... bio balls if you still have them!) something with a bit of surface area... doesn't have to fill the tank... or better by far, to read over our Pond subweb re biological pond filtration, and incorporate a non-pressurized (open) bio filter... with some mechanical capacity to save your sanity and pocketbook from the hassles, costs of the current cartridge... Koi do require clean, oxygenated water... continuously... If you should switch these out for "dirtier" fishes or no fish at all, the situation would/will be different. Bob Fenner>
Re: Koi pond no filter?
Thanks Bob. I searched for open bio pond filter and didn't see it. <Please see the pond articles and FAQs files here: http://www.wetwebmedia.com/PondSubWebIndex/Pond%20Sub%20Web.htm ... "filters for biological ponds...> Can my pressurized filter be switched to an open filter? <No> Or... this pond in question has a separate pond (higher elevation) of about 300 gallons that spills in to the main pond. What about turning this 300 gallon into a bio  filter? <Can be done> If I filled it with rock and planted heavily? <Yes> Or if I filled it with bio media? There has to be a way to eliminate the sand filter and run naturally I would think. Again it is clear and healthy as it is now (6 years old) and that's running the sand filter only 9 hours a day. Thoughts? Thanks Gregg <Many. Bob Fenner>
Re: Koi pond no filter?
One final follow up question please. I am taking your advice and using the upper pool to create a bio filter for the main pond and getting rid of the pool sand filter. I'll be dividing the upper pool in half with bricks to create an area like the La Jolla guy did (rock and bio balls on top of a mesh screen) Question: do I need to seal the bricks and mortar to stop lime leeching? <Mmm, probably not. Just use "plastic" cement in your mortar mix, rinse, let it go covered over for a day with tapwater, drain... or add a bit of acid to the water (not the lower basin of course) during the day to leach the alkalinity...> this will be a small wall maybe 2ft high by 3ft across. If I use "old" bricks will they be lime free enough? If I have to seal what should I use? Thanks again. Gregg <No sealer needed. Bob Fenner>

Pond filter Hey guys thanks for all your help on my saltwater questions. I am having a couple beers and thought I would pick your brains a little. I am now changing gears and started my first pond in the back yard. It is only about 200 gallons of freshwater. I think it is too small already but will wait until next year to expand. <Good and lucky that you have this as a possibility> I have read through the filtration section of your site and decided on building my own filter. I would like to use a 16 gal Rubbermaid container. I would like to run the water through the top lid of the Rubbermaid and first through a filter pad. My question is what type of substrates do you recommend next? The articles I read say to use 3/4'' rock with 3\8'' pea size on top. I have a lot of crushed coral from an old saltwater tank would that work for the top layer? <Mmm, not a good idea likely in this setting... too alkaline.> Is there better types of rock to use for the top and bottom? Or would it be better to make baffles and have 2 separate sections? <This is such a small filter for such a small volume of pond water that I would go with just the smaller (pea, nominal 1/4" diameter) "aquarium gravel" (the natural crushed Chondritic granite variety) under a layer or two of "batting material" (Dacron/polyester from a yardage store... you can cut to size with scissors)... and if possible, I would make this "reverse flow", pumping the water in/under the gravel and have it overflow over the top of the Dacron... with thru-hull fittings perforating the Rubbermaid container...> My pump will probably be pumping around 1000 GPH. It is submersible but it is an extra I have around the house. Is this too much flow for this filter? <No... about right> How deep should each layer be with this water flow? <For regular or reverse-flow leave an "empty space" on the bottom, perhaps using a piece of cut "egg-crate/louver" supported by PVC pipe, fittings, cover this with a layer of plastic screen door material (you can get all this at a Home Depot, Lowe's or such), several inches of the pea gravel, then the batting material, leaving a handful of inches at the top for accumulation of water out to the (good-sized, at least 1 1/2", better 2 " ID thru-hull overflow> If this is too much flow for the filter should I split the flow and have some return directly to the pond? My plan is to have 3 Koi and a Shubunkin and a few plants. Any advice would be greatly appreciated. <Good idea to plan in a "tee" diverter with a valve on the discharge side of the tee going back to the pond to provide circulation and control over flow to the filter> One more question: Is using a little salt in the water good for these fish. A guy I work with said his neighbor has a pond that is 2000 gallons of saltwater and he breeds Koi in it. I assume he means it has a little salt in the water not a marine tank. Thank you!! Walt <Koi and goldfish can tolerate a good deal of sea salt concentration... not a good idea to keep them in such all the time though... a little salt is better. Bob Fenner>

Knee Deep In Sand? Or, Just a Few Inches Deep? Hi all: <Hi there! Scott F. here today!> Please can you tell me if it is worth putting sand in the bottom of my weirs to encourage bacteria to grow, if so what thickness of sand do you recommend both weirs are 4inches by 4 inches . Regards, Ian Marvell <Well, Ian, beneficial bacteria will grow on all types of surfaces, including the weirs themselves! A substrate like sand offers a lot of surface area for them to colonize on, of course, and bacteria can grow on even a very shallow layer of sand. For maximum denitrification capabilities, I'd go with a depth of 3 inches or more. Hope this helps! Regards, Scott F.>

New Pond Hey crew! <Hey! Gage here this evening.> I just got a pond from my Uncle that is roughly 175 gallons. It is a pre-made plastic frame. Couple questions: Do i need any additional liner? <Nope, the performed plastic pond should be fine by itself.> Am i correct in thinking that in the hole i should fill it with sand to let the pond settle? <It is a good idea, and watch out for any sharp rocks in the hole.> And finally, can you suggest a good filter, because the one i have is really old and filthy? <Old and filthy, that's how I felt on my birthday.  I have not shopped for a pond filter in a while, you have a couple of choices, you can get the kind that has the media/bio balls and all that in a container that drops into the pond, with a pump, and usually fountain making do-wacky (ok ok, its late, it may have another name besides do-wacky).  The type of filtration I prefer would consist of a pump in the pond pumping out to a container (large rubber maid?) filled with media, then returning to the pond.  Check out these links for more info http://wetwebmedia.com/PondSubWebIndex/inpdfilters.htm http://wetwebmedia.com/PondSubWebIndex/biopdfilters.htm http://wetwebmedia.com/PondSubWebIndex/pdfiltmedia.htm  > Thanks a ton if you answer any of these. I normally read about my dream fish, the black-tip reef shark, instead of ponds. <Best to read about the black tips and keep a pond IMO.  Heck, move the pond indoors and/or heat it and fill it with cichlids, you would be the coolest person on the block. Best of Luck, Gage> (this will be a freshwater, outdoor pond.) Thanks a ton Ryan  

Bird poop in Small Goldfish Pond II - 8/15/03 Thank you for answering Anthony. I will not assume it is bird droppings. The pond's life is almost 8 months. There is a small pump and sponge filter and I do water changes every couple of months. I have two goldfish, water lily and lots of water lettuce, and oxygenating plants. Am I on the right track. Marty <the sponge filter may be too small, and the water change schedule is very modest. Some pond keepers try to do at least 10% weekly. 25% monthly at least. Especially during warm weather. Best regards, Anthony>

Filtration/Pumps Hi: We are setting up three small separate ponds in rubber maid type containers. One is about 25 gal, one is 110 gal, the other is 40gals. We want the 25 gal to flow into the 110, and the 110 to flow into the 40. We plan to have a few fish in each. Do we need a separate filter for each pond? <Mmm, no. You can set all up in just one container (likely the last so the same pump can be used for recirculation> Can we use just one filter and pump to recirculate? <Oh, yes> What do you suggest? <There are about all possibilities covered on our Pond sub-web... maybe you can get by with a foam cartridge intake filter (as by Rena or Tetra) if the system is "balanced" and out of much direct sunlight> The lowest pond is about 2 feet below the top one and about 16 feet distance, with the other pond in between. Thanks for the help. Your web site is great! <Thank you for your kind words. Bob Fenner>

Re: water fall/filter Hi Bob My name is Andrew Girard. I met David Korhonen at the Landscapes Ontario trade show. He had a water fall that doubled as a filter, I was wondering where I could purchase such an item. I am new to the pond world. I have a small pond with no filtration system. David told me that the water fall filter would be the best for the type of pond I have, I just can't remember the type and name of the filter. If you could help me I would appreciate it very much. Thanks Andrew <Mmm, well there are a few companies (like Pondscapes) that make or re-sell such fiberglass and resin fall/filter units. I encourage you to consider other possibilities though (if you have the space), placing a "large as possible" filter elsewhere in your filter flow-path... much easier to service than "fall-types". Bob Fenner>

Biological filters... for ponds Bob, Sorry to bother you. I got your address from the Wet Web site. I am new to the pond game and need some direction. I have a 60 gallon plastic pond, 15 paradise fish <Macropodus opercularis, some of my faves.> , two water lilies, four irises and a small batch of elodea. There is also a pleicotomous (sic) <Plecostomus> and some snails. I am interested in building my own biological filter and would like to know the best place to look for plans or specifics. Is there a book you recommend as well? Also the fish colony is nearly 15 years old and this is their third transplant. I am a capable plumber but I have a very low budget. I am thinking of using a square plastic bucket apprx. 4 gallons (it used to hold cat litter) for my filter container. thank you very much for your time, Curtis Whatley Mission, Texas >> <Do take a look back on our WWM site: Home Page for a good rundown on how to build your own filter... you have a good start being a plumber (my dad was one as well), and your container should work as a structure. Bob Fenner, who does have a water gardening book done, but it's not in print, yet...>

Aquatic Gardens

Ponds, Streams, Waterfalls & Fountains:
Volume 1. Design & Construction
Volume 2. Maintenance, Stocking, Examples

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by Robert (Bob) Fenner
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