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FAQs on Pond Filtration Media

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

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Aquatic Gardens

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

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by Robert (Bob) Fenner

How often do I change the filter media?  04/21/11
Can you please tell me how often to change the filter media in a pond? I have a foam pad and a biological filter with bio-balls.
Thank you!
<Mmm, highly variable, but for many types, situations, rinsing out such media once a week is prudent. Do read here: http://wetwebmedia.com/PondSubWebIndex/pdfiltmedia.htm
and the linked files above for input. Bob Fenner>

Zeolite, as a pond filter media... pressurized   11/11/09
Would a 100% Zeolite filter interfere with biological filtration as it removes ammonia?
<Mmm, minimally in actual practice. What seems to occur is that detritus, perhaps even spaces amongst the Zeolite serve as substrate for nitrifying microbes in time; sometimes a very short period of time>
The Zeolite filter also filters down to 1 micron
<? Really? Is this a specific product?>
as it removes ammonia. Could there be any problem?
<Again, doubtful>
We have a 750gal Koi pond with a very large biological filter. We are trying to keep particulate matter from entering the biological filter and going back into the pond.
<Mmm, most folks avail themselves of some mechanism ahead of their biological filter... a mechanical screen/sieve like media (e.g. "batting material"), and/or a sedimentation chamber that has a manual or automated draining (cleaning) process. Are you familiar with these? Bob Fenner>
Re: Zeolite  11/11/09

Thanks Bob for your quick reply. I have pasted in my communication with the Zeolite Company.
<Okay, will look>
I have read about Matalla use in stages. I intend to try it by converting a cartridge filter.
<Much better than cartridges... they clog way too easily, quickly...
Expensive to maintain, and cost even more per gallon of water moved through them!>
I'm a designer in the pool business
and enjoy this process.
<Ahh, I was a contractor installing water features for several years. And a longer-time content provider in the Nishikigoi industry period>
We were just concerned that a prefilter of all Zeolite would interfere with the biological filter.
<Not a worry I assure you>
The concept of down to 1-3 micron filtration (similar to DE) with Zeolite plus removing ammonia in ponds is intriguing.
<Mmm... I really don't think this is a practical approach... Diatoms/Bacillariophyta "work" due to characteristics of their skeletons... being "holey" and chemical inert (principally composed of Si02)... Zeolite Clays... I don't think will really work. Ammonia is better addressed biologically through complete, vigorous circulation moving all water through an "open" media.>
It is now available for swimming pool filtration as a replacement in sand filters. Dick
<Interesting... Will take a look/see at this as well. Thank you, Bob Fenner>
Begin forwarded message:
> Yes zeolite is wonderful filtration media for Koi ponds if it is installed correctly. Ammonia is harmful to all fish see link below.
> http://koiclubsandiego.org/library/ammonia.php
> As for sales literature it is not mass marketed due to the lack of  potential market size.
> As for converting a cartridge filter to a sand filter, I am not sure how that could be accomplished. I can only recommend replacement ratios of ZeoSand to sand filters that have manufacturers recommended fill rate.
> So if you are creating your own filter to use ZeoSand then I am afraid I really can't suggest/recommend the proper fill rate other than to say that most sand filters media bed rarely extends past half way in the tank.
> Thanks
> Todd
> Subject: Re: CONTACT ZEO, INC.
> Thank you for your quick reply. I need to know specifically:
> 1- Is Zeolite a good and safe mechanical filter for Koi ponds? I can find no sales literature.
> 2- Will removing too much ammonia harm the fish?
> 3- I can convert the cartridge filter to a sand filter. Where do you see a problem?
> Thanks for your indulgence,
> Dick
Todd B Hamilton wrote:
>> ZeoSand may be substituted for sand in any filter designed for use of sand
>> as its filter media. It will replace sand at a 50% ratio. (Example if a sand
>> filter requires 200 lbs of sand you will need only 100 lbs of ZeoSand).
>> You can't just replace your cartridge with ZeoSand. You must have a filter
>> designed for sand as its filter media. Also follow installation instructions
>> concerning cleaning and wet-fill of ZeoSand prior to filtration.
>> http://www.zeoinc.com/zeosand4.html
>> ZeoSand will remove ammonia but it will eventually load up with the ammonia
>> at which time you will need to refresh the ZeoSand by soaking it in a 10%
>> salt solution for at least 4-6 hours, then rinsing all saltwater from media prior to returning to filtration.
>> http://www.zeoinc.com/zeosand5.html
<<Folks aren't going to do this... good gosh! BobF>>
>> In a swimming pool this would be accomplished by backwashing to waste. In a
>> Koi pond you may not be able to do this so it must be done manually if your
>> desire is to continue to remove ammonia. If not it will continue to filter
>> other debris until cleaning is necessary.
>> If you have further questions feel free to contact me at anytime.
>> Todd B. Hamilton
>> V.P. of Development, ZEO, Inc.
>> thamilton@zeoinc.com
>> zs: ZeoSand Filter Media
>> comments: I can find only limited info on Zeolite filters for Koi pond
>> mechanical filtration. I maintain a 750gal Koi pond. At present I am using
>> a 50sqft cartridge filter before the biological filter. Can I replace the
>> cartridge with Zeolite? Will it remove too much ammonia? Would it be
>> adequate as a mechanical pre filter? The filter is about 1' x 3'. How much Zeolite would I put in?
>> Thanks,
>> Dick
Re: Zeolite... referral... Read re gen. pond filtration methods   11/11/09

OK. I would not be using the cartridge filter. I would be replacing it with 100% 1-3 micron Zeolite. The filter runs are longer than sand even though sand only filters down to 20-35 microns. Sounds counterintuitive doesn't it. The Zeolite can of course be recharged to remove ammonia, but if it weren't, I still think it would be a good prefilter. You like the gradated Matalla better?
<One L>
I'm looking forward to your evaluation.
<My input is archived here: http://wetwebmedia.com/PondSubWebIndex/Pond%20Sub%20Web.htm
Re: Zeolite  11/11/09

Thanks for all the info. I was particularly interested in your evaluation of what the Zeolite Company has to say and offer. I will read all your articles.
<... again; the physical and chemical properties of Zeolites make them not useful for substitution in DE filters, and far less suitable in sand filters... and not useful at all in place of cartridge elements in cartridge filters. Read. BobF>
Re: Zeolite  11/12/09

Oh Bob,
I am doing a very poor job of communicating and a worse job of understanding. Probably it's age and lack of knowledge.
<Maybe I'm just not quite as awake as I think I am...>
I would not substitute Zeolite in a DE filter. I would use a sand filter with Zeolite instead of sand because of the finer filtering qualities, longer runs, and removal of ammonia.
<Again... due to being more/too three dimensional, "melting" vs. silica/tes, I don't think Zeolite/s are practical... but try them out for yourself and see>
This is done regularly for swimming pools.
<... biological systems are very different. Among other aspects, they're variably reductive (as in RedOx...) and their acidity will dissolve the clay>
I really want to know if this is good or bad for a Koi pond and why.
<Their NH3/NH4OH capacity is not limitless... they're not catalysts, but absorbers...>
I am having difficulty understanding and putting together your 2 responses directly below.
I have to hand it to you, you are very indulgent and courteous in this matter.
<Sorry for being so daft, but I am wondering if we're starting "too far forward" in this conversation. Have you actually ever kept a biological pond? BobF>
Re: Zeolite  11/12/09... still not reading...

What I'm talking about is Zeolite crystals. They are permanent and able to be regenerated for ammonia removal.
<... Dick... people/humans are NOT going to do this... Please don't write... READ. I have a book in print through TFH publications on ponds that would give you a good grounding... or just peruse WWM>
If they weren't regenerated, they would still be a very good filter agent--infinitely better than sand.
You finally saw that I don't know much about biological systems. My son does. I'm trying to work out a pre filter to minimize junk in the biological filter and produce super clarity to the pond water.
I find this all very interesting and plan to learn more.
<Good. B>
Re: Zeolite, in rel. to pond filtr.   11/14/09

Well Bob, It looks like I do have one more question. After your suggestion to READ and not WRITE, I made an extra effort to find info on your website about mechanical filtration in ponds--could not find anything.
<I suspect Bob was hoping you'd start off with articles like this one:
I have also been all over the internet. My original purpose in contacting you was to find out about Zeolite filters and polished pond water.
<The two things aren't related, and I suspect that was Bob's point here.
Zeolite removes ammonia; that's it. "Polishing" water is mechanical removal of silt particles, and perhaps in the case of ponds UV sterilisation to kill off any floating green algae ("green water"). Zeolite isn't usually economical to use except for very small aquaria where the pH is sub-6.0 and so biological filtration isn't possible. In a pond, you'll get far better ammonia remove from the biological filter and the photosynthesising plants.
Zeolite eventually becomes saturated with ammonia, and typically in just a few weeks. It's recharged by soaking in brine, and obviously you don't want it to be recharged in the pond because all it would do is release the ammonia again! Plus, over a few weeks it gets clogged up with silt and bacteria (saprotrophic ones, not just chemoautotrophic ones) and this reduces its surface area. Again, this is why you have to replace zeolite:
even if you recharge it, it eventually loses the optimal surface area to volume ratio it has when fresh, and becomes functionally worthless. Folks will happily sell you zeolite, but it really does have a very limited range of applications in fishkeeping. Hospital tanks where strong antibiotics are being used, pH 5-6 freshwater aquaria, that sort of thing.>
That was it. It also seemed logical that reducing ammonia and keeping particulate matter out of the biological filter was a plus.
<Yes, these are both good aims, but they aren't related concepts.>
Perhaps you could lead me to a website or file addressing this concept.
<See above.>
I sense that you grow weary of our communication. I won't be taking up any more of your time.
<I fear Bob never wearies of communication... literally thousands of e-mails get answered here every year by a crew of maybe a dozen people.
What does get tiring, I admit, is answering the same questions over and over -- and in my case that usually involves sick Bettas being kept in teacups by undergraduates! But I digress. Reading before writing is always a plus, but generally, we're always happy to hear from people, no matter what. If we didn't like it, we wouldn't do it.>
I thank you for help. It has lead me on to more education. I will read all of your articles.
<Cheers, Neale.>
Re: Zeolite  11/14/09

Now that's a real good answer to my question.
<Happy to help.>
Thank you for being so complete and thank Bob for not just giving up on this matter.
<Will do so.><<I never give up. RMF>>
You provide a very good service.
<Not sure "service" is the word, since we don't get paid for this, but we're certainly happy you appreciate what we're trying to do here.>
<Cheers, Neale.>

Using carbon to remove an unknown chemical. Pond filtr. -- 04/22/09
Hi, I have a pond that has been in 'use' for over a year now. the problem is that I didn't feel like working with it previously do to an illness that I have, so essentially it was left for my family to care for. Due to mosquito issues my family added a floating chlorine realizing device and several dosings of bleach last summer. I now wish to work with my pond and have tried adding some paradise fish to it. The paradise fish look horrible only minutes after being added and I'm unable to locate them the next day. I have also been having some problems with duckweed and salvia that I have contributed to the sun before I noticed the problem with the fish.
So here's the condition of the pond. Ammonia and nitrites are 0, I didn't test nitrate yet because it wouldn't account for the speed of deterioration in the fish that I have been noticing, and the API test is kind of a pain. PH is high, about 7.5-8, but again, while not ideal for the paradise fish, I don't see it killing them. The duckweed is mostly dead, but there are a few that are staying green, and there are a few aquatic insects currently alive at this time. I'm thinking that there is some chemical in the water that is causing the fish death, and that the duckweed and insects are only surviving in small numbers. 99% of the duckweed is dead, and I'm guessing that there should be a lot more insects then there are, but only a small number are surviving. As to whatever may have been released by the floating chlorine releasing device or something extra in the bleach I unfortunately don't know.
<Mmm, possibly just the excess chloride... easy to remedy...>
There's even a possibility that something else might have been added to the water last year, and forgotten about, so no one mentioned it.
My plan was to use carbon to remove anything that might be left.
Do you think carbon would be enough to remove an unknown toxin? I was thinking 30lb, pond is approximately 160-180, three uses of 10lbs each or so. i will be making my own addhawk
<Heeee! Ad hoc?>
 filter for this purpose so if you have any suggestions on dosing I can probably accommodate it.
I would eventually like to release some Xiphophorus birchmanni which would enjoy the high ph, but I'm afraid to until I start seeing some better results with the paradise fish. Thank you for any help, Christian.
<Much cheaper and surer to dump most all the water out and just re-fill it anew. Bob Fenner>

Pond Dried Up... Oh no!  Holding tank set up, op.  10/23/08 Hi, I'm contacting you for this reason: my pond dried up. I had no clue it did until I returned home from college one evening and my mom asked me to help her collect the fish. They were very easy to catch, if that gives you a hint of how shallow the water was. My mom knew of my love of fish and asked me if she could use my 30gal tank to hold a small portion of the fish chosen (possibly a max of 30). They're all small specimens, and only a max of 10 fish are at 1". I'm disappointed in my mom because she doesn't even know the type of fish she bought. I don't know either because I'm more of a saltwater enthusiast. My mom thinks they're bass and minos so I'll just go with that. <Bass eat minnows, so mixing these fish together isn't exactly recommended.> I have two power sweeps (yes I know they will get stuck sooner or later) that I'm willing to donate to my mom that get 270gph and I was thinking of getting an Emperor Bio-Wheel (400gph) so that I can use filter media (e.g. carbon to make the water clearer). <Carbon doesn't make water clearer. Carbon removes dissolved organic chemicals, and in freshwater tanks is almost always redundant provided you perform regular water changes. Concentrate on mechanical media (which removes silt) and biological media (which removes ammonia). Unless there's some overwhelming reason to get a hang-on-the-back filter, I don't recommend you choose one; standard external canister filters are better value and more flexible, and don't force you to use proprietary filter modules. Sponge filters are also very useful when maintaining small fish for short periods.> I also will be using reverse-osmosis water, and all the other correct electrical devices (e.g. heater). <Why are you using RO water? Remember, pure RO water is lethal to freshwater fish. If in doubt, stick with tap water treated with dechlorinator. This should be reasonably close to the water these fish were inhabiting, assuming your water supply gets the water locally. Do not use water from a domestic water softener.> I'm going to purchase an array of fish food so that the fish will have a varied diet. <Minnows and bass obviously eat different things, but wet frozen bloodworms and mosquito larvae should work well for both, at least while the Bass are small.> Water changes weekly (keep pH at 7... it's a safe number for freshwater I'm guessing). <Preferred pH actually depends on the species in question, but pH 7 should be fine for these species.> I wanted to know if allowing the water to cycle 24hrs would be good enough to then introduce the fish? <You can't "cycle" a tank in a system without ammonia. By definition, cycling is how ammonia-consuming bacteria get established. There are products on the market (like Tetra SafeStart) that supposedly "instantly" cycle a tank when used correctly. At least some of these (like Hagen Cycle) are of questionable success in this regard, but better than nothing. In any case, your best bet is to grab some live biological media from another filter on an established tank and put into your chosen filter. Do read here: http://www.wetwebmedia.com/FWSubWebIndex/fwestcycling.htm > We're keeping them in buckets for now outside (very hardy to those conditions; very different from saltwater :D). And I wanted to know if I could keep the tank with a bare-bottom? <Fish aren't wild about bright colours underneath them, so plain glass or white plastic don't go down well, and the fish get scared easily.> I know the algae will help within the substrate at the bottom of the tank but we're only doing this for the winter so that when our pond gets back to its regular size the fish will be reintroduced into their natural habitat. <I'd scatter at least a bit of smooth silica sand or gravel. Just enough to cover the glass.> Thanks for the help, Jeff <Cheers, Neale.>

Chicken Grit, pond filtration   6/4/08 I just built a new pond. Its about 25 feet long, 12 feet wide at the widest, tapering to 5 feet wide at the narrowest. It's 18 inches deep at the narrow end tapering to 30 inches deep at the wide end. It's roughly 2200 gallons. I'm using an Ebara pump, rated at about 4300 gph to an 18 inch Hayward sand filter filled with 100 lbs of crushed granite Chicken grit. The pieces are roughly 1/8 inch to 3/16 inch. <Mmm> I've only had the filter up for a couple days and the water is starting to clear. I saved about 100 gallons of my old pond's water for a bacterial boost. <Good technique> Unfortunately we've been hit by torrential rains since I filled my pond and have been unable to complete the waterfall or anything else, yet. I was wondering how well the crushed granite would perform over pea gravel. <Both can be problematical... in terms of "compacting" and channeling... lighter media is highly preferable> The pea gravel sold in my area is more like ½ to ¾ inch gravel and with pieces that large, I don't see how they will do much filtration. I backwashed the filter this afternoon and the water was still relatively clear. I don't have any fish in this pond yet. My son managed to catch all my Koi from my old pond and carry them like a squirmy bluegill to the horse tank for safekeeping. Unfortunately they died from the trauma of an overzealous teenager's handling. Any idea you can throw my way would be most appreciated. <Best to scoop up not-so-handled "medium" (a foot, foot and a half) Koi in thick (4 mil.) fish bags (see your dealer or save old ones) and move with minimum water. Larger Koi still, esp. ones that have been handled from time to time, can be picked up, carefully, from underneath... there is a great deal that can be related re technique here> I'm kind of a jack-off-all-trades, and I prefer to make whatever I can. My drywall bucket bio prefilter is my first engineering marvel and is still in use in my new pond. It's installed after the mini skimmer with a 900 gph pump discharging toward the waterfall site, so there aren't any dead spots. <Ah, good. Again, I would look into "more appropriate" filtration methods here period. Pressurized filters, the pumping to run them... is too expensive and inefficient in this day and age... Do check out the Net, libraries for modern books, articles on other means. And we'll chat if you'd like re. Bob Fenner>

Pond Filter Design Hi Robert, I read your article in Wet Web Media.com. I think your ideas make a lot of sense. Do you have more details on the construction of this simple idea including the filter media to use. <Do... in my files at the S. Cal. res... but am out of town... Are you looking for something in particular? We started with encouraging folks to use crushed rock, graded... some people advocated the use of igneous... we eventually found, cut with a band saw, plastic honey-comb used in cooling towers...> Thanks in advance. I'm installing an 1100 gal fiberglass pond. Best regards, Horst Riedner <Bob Fenner>

Rocks, bricks... as Pond Filter Media Thank you for offering to answer my questions. I am considering using refractionated bricks or cinder blocks (broken up) as a filter media. Will either of these hurt the fish in any way? Do you see any reason why I should not use one or the other? Thanks! Cindy <It's possible these materials may alter your water pH and alkalinity... but easy to test for... and it may well be that your source water is deficient in alkaline reserve and this might well be a good way of bolstering/supplying it. I definitely would do a chemical AND "bio-assay" with a bit of the proposed filter material in a container, testing the water before and after for pH and alkaline reserve... and adding a few (likely "feeder" gold)fish to the mix to see how they do. Bob Fenner>

Pond Filters, media Last March(03) my wife and I purchased a 15ac. 200 year old farm house (NC).  The last owner had had the "yard guy" create a 10,000+ gal. fish pond. We were told we only had to clean the filter two or three times per year. <Some types of systems, yes... some even less frequently... depending on what one means by "clean"> The filter is a circular gray(3 ft dia. and 4 ft deep), 250/300 gal., up flow system with seven, 2 inch thick plastic fiber mats. I cleaned the filters every 30 days during the first summer and let it go during the winter (5 months/ Nov. thru march). There were no fish in the pond to start but my wife added feeder goldfish 1/2 through the summer and they have done very well. We now have 50 to 100 " good size" goldfish.  My question is... what is the best filter media to use to keep a pond this size clean. Ease of cleaning is my highest priority. <Good question... as you will find, there is an article/discussion of various pond filter media archived on WWM: http://wetwebmedia.com/PondSubWebIndex/pdfiltmedia.htm Criteria for your particular choice include the make-up of your water (chemical, physical), cost/availability of media there, the degree of "cleanliness" you desire... and what other means you're willing to apply (e.g. other filtration modes like UV, ozone...) to get you where you want to. What you have now is likely 80 some percent of so what you can hope to achieve with the current set-up... and I might just add some live plant material and leave the rest as is. This will be fine along with partial water changes, vacuuming of debris/overburden during warm months and careful feeding of your goldfish, to keep the system biologically (and aesthetically) sound. Bob Fenner>

Biological Filter Hi Robert, I'm in Australia and would appreciate your advice. I have just been given an old fibreglass rainwater tank (approx 1100 gals & 8 ft in diam.).  I am going to use it as an additional biological filter for my 10 yr old 6000 gal Koi fish pond. It will be an upflow system through a crushed rock medium gravity feeding to my existing filter (it will have a bottom drain for cleaning). In the future, if needed, I will add a vortex settlement tank at the start of my system. <Many possibilities... the settlement one is good... with brushes, some sort of material as a "pre-filter"... maybe Dacron "batting" material from a yardage store.> The outlet from this new tank will need to be about 4 ft from the bottom to enable gravity feed to existing filter. I have 2 questions:- 1) I have read varying reports on filter media depth and would love your perspective on the optimum thickness? <Mmm, depends on make, diameter, and to some extent on "roundness" of the media. Have you read over this: http://www.wetwebmedia.com/pndfltmedia.htm re filter media for ponds?> 2) Because of depth of water in this new tank (4 ft) will it affect bacterial growth if say there was 2ft of water over the top of this media? <No problems... better to have a large amount of water than have difficulties with too much media, clogging/channeling... Other possibilities include stratifying media types, grades over a screen... even using lightweight "beads" or plastic "rings" as per sewerage treatment... even floating plant material in the water column above (like hyacinths, Myriophyllum... many more). Some of these are covered on WetWebMedia(.com) under the "Planted Aquarium" index> Thank You very much, David McPherson <Let's keep chatting this over if anything is unclear. Bob Fenner>

pond filtration hi, Just wanted to ask for your opinion on the emperor aquatics bag and bio pond filters. (http://www.emperoraquatics.com/pondbagbio.html)  thanks <Of products of their kind, they are superlative. I have used these bags as "first lines of particulate and filth (fish, invertebrate wastes) in aquaculture, live-holding facilities for many years. They really work. Bob Fenner>

Foam Filters? (this time for ponds) Hi Bob, I recently bought a home with a small Koi pond and am trying desperately to make sure they survive... My problem is this: the filtration system pumps the water up into a tank on the bottom of which are two layers of polyurethane foam with a hole cut in the center through which the hose from the pump goes pumping the water under the foam. <Yikes... hard to clean> Near the top of the tank is a hose returning the water to the pond. The previous owners left instructions on when and how to clean the tank and replace the foam however I am running out of foam and can not seem to find a source of this "biological filter foam". <You can get it from a yardage store (as in sewing) or furniture or large hardware store outlet... it's likely just open-cell polyurethane sheet... can be cut in a few ways> Can you recommend a place to get more or a better material through which the water should filter. <Yes... look into "batting material" from the yardage store...> I seem to be in trouble because for a few months an extra fish temporarily lived in the small space over taxing the environment leaving a lot of algae and other plant life living on the pond liner (on the sides)and causing the pump and or hoses to slow the water flow to a trickle every few days. The only way I seem to be able to clear it up is to force water through the hoses and clear them but every 3 or 4 days I seem to have to do that again. This was not true for months before the now gone visiting fish over taxed the pond's capacity... What do I do now? <Mainly a seasonal problem... with cooler weather, less sunlight all should settle down> Replace the filter material more frequently until it clears up or what? Help! Thanks for your time, Jim Gallagher <I would really like to start way, way back (watch yourself, don't fall in the pond...) and have you read through the Pond Index on our site: www.WetWebMedia.com: http://wetwebmedia.com/ponds.htm  and particularly all the sections on pond filtration, starting here: http://wetwebmedia.com/pndfilts.htm Don't despair, and let's not "band-aid" what you have here, but work toward a better (cost to run, time, overall water quality improvement) solution with me here. Bob Fenner>

Aquatic Gardens

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

V. 1 Print and eBook on Amazon
V. 2 Print and eBook on Amazon

by Robert (Bob) Fenner
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