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FAQs on Marine Freshwater Quality involving Nitrates 2

Related Articles: Nitrates in Freshwater Aquariums, Establishing Cycling, Freshwater Filtration, Know Your Filter Media, A Concise Guide to Your Options by Neale Monks, Setting up a Freshwater Aquarium, Tips for BeginnersWater Quality and Freshwater Aquariums

Related FAQs: Nitrates 1, & FAQs on FW Nitrates: Importance, Science, Measure, Sources, Control, Chemical Filtrants, Troubleshooting/Fixing, & Ammonia, FW Nitrites, Biological Filtration, Freshwater Nutrient Cycling, Establishing Cycling 1,


High nitrate levels in pond and aquarium       4/18/20
Hi Bob and Friends,
<Hello Annette.>
Recently my platys have been dying. All my other fish seem ok. I did a water test kit from API and the pH was 7.6, but the nitrates were at 160 ppm, which was the highest level.
<Yikes! That'd be the reason. Fish vary in response to nitrate. Cichlids and Mollies are very sensitive, and long-term, anything above 20 mg/l can cause health problems. Most community fish will be fine up to 40-50 mg/l, and characins and catfish seem to be, on the average, among the least sensitive fish (which probably explains why they were old favourites for community tanks up to the 1970s, when people avoided water changes).
Platies are likely to be more like Mollies, so your high nitrates could easily be the problem.>
Is there anything I can do?
<First up, a water change. Do a series of changes across the next few days, such that you change 30-50% of the water each time. Try and keep water chemistry and temperature steady. After a few days, nitrate should be close to whatever your tap water level happens to be. Secondly, review stocking, tank size, and feeding. The old rule that says "an inch of fish per gallon" is pretty good, so if you had, say, 10 platies, these are about 1.5-2 inches long, so you'd need 15-20 gallons to keep them. Any additional fish would be added to that, so if you had, say, six Corydoras catfish, each about the same size, they'd be another 9-12 gallons, so together your tank would need to be at least 24-32 gallons in size. This rule is conservative, but works really well for small fish in the 1-3 inch size range. Feeding should be moderate, and as a rule of thumb, small community fish need a 'portion' of flake about the size of their eyeball each meal. Feeding once or twice a day is fine, and for fish like Platies especially, just letting them graze on algae (or softened vegetables, such as spinach, peas or
cucumber) is a fine way to round out their diet. Overfeeding fish doesn't kill them by poisoning them or blocking their stomachs or something, but too much food does mean the filter is working harder, and as you can see, the end product of filtration, nitrate, isn't non-toxic. That's why we do water changes every week or two: to dilute that nitrate. Fast-growing plants (such as floating plants if you have indifferent lighting) can be
really helpful too, since plants absorb nitrate.>
The pond was the same. I saw a De-nitrate water additive.
<Don't waste your time with additives. Water changes do a massively better job, for much less cost. Honestly, while there may be niche applications where denitrification is relevant to freshwater fishkeeping, there's
otherwise no reason to get bogged down in this side of things. Instead limit stocking, ensure the tank is nice and big, don't overfeed, and do regular water changes. That's all you need to do, and it not only works well, but doesn't cost anything!>
<Cheers, Neale.>

Ammonia, Nitrite & Nitrate Units of Measure     4/10/18
Hello Crew,
<Hey Ray>
I have a 210g, probably considered overstocked, mixed Malawi tank. The tank is filtered by a submerged media sump with a six times turnover. I use Hanna meters for my chemistry checks. The ammonia, nitrite and nitrate
meters all measure using the -N unit of measure (NH3-N, NO2-N & NO3-N).
The unit of measure for ammonia and nitrite are not relevant since the goal of both is to maintain 0ppm. Nitrate is the one causing me some thought. The tank consistently runs 10 - 30ppm NO3-N and I use this value to determine water changes, as it approaches 30ppm I do a 50% WC usually every other week. But if I apply the conversion factor (4.4) to these numbers my ranges are 45 - 130ppm in which case my WCs should be happening probably twice per week. I recently read the article, Nitrates in Freshwater Aquarium Systems
by Bob Fenner, which stated "Do check your test kit though almost all are nitrate ion types on the market nowadays..." I'm guessing doing the conversion on NO3-N > NO3 is what I should be looking at.
<Yes; agreed>
The tank has been running in its current configuration (mixed Malawi) for 2 years, before that it was a planted discus tank for maybe 8 years. Being retired gives me time to think, maybe too much. Should I take the attitude, "if it ain't broke, don't fix it?" Looking for confirmation/disagreement.
Raymond M Sugel Sr
<Were it me, mine, I would increase the number/frequency of water changes as you state (twice a week; with pre-mixed (for pH, salts if you use them) stored water. I encourage you to look into the possibility of tying this
tank in with a good size/volume sump as well, perhaps growing live plants there, incorporating a deep sand bed for denitrification; utilizing and out-gassing the excess NO3. Bob Fenner>
Black Ghost Knifefish; hlth., NO3 file       11/24/17
Hello Crew,
Stumbled onto your site, read some stuff that sounds very helpful.
I have a large about 30cm long single BGK fish, I had it now for a few years in a 645Ltr. mostly African (both Tanganyika/Malawi) a pair of buffalo heads, clown loaches and Chinese Glass cleaners.
<Quite a mix>
All doing well.
At one stage awhile ago I was concerned about Nitrate/ Nitrite but have given up, could not get it right, hence small regular water changes, water always clear, no diseases, fish have been happy, some have bred
For some reason I have noticed BGK with swollen belly not eating, see him more often than not. Hangs vertically near the water outlets from the filter & not in usual hiding hole. BGK fish was large when I bought him, could he be getting old? But why the swollen belly?
<Perhaps "just" over-eating... could be a blockage, tumor... even a bacterial et al. infection>
I would greatly appreciate any advise regarding my Black Ghost Knife fish, he’s cool.
<I'd read on WWM re NO3; endeavor to keep it under 20 ppm via various methods, introduce a "laxative" food item (e.g. Daphnia, Artemia) to the BGK for a week or so. Bob Fenner>
Re: Black Ghost Knifefish     11/29/17

Thank you Bob,
<Welcome Gavin>
Knife fish died. I'm thinking tumor or blockage. I don't feed fish for days at a time sometimes due to shifts I work.
<I see>
Appreciate you getting back to me though.
Thanks again
<Thank you for this follow up. BobF>
Re: Black Ghost Knifefish; now Nitrate f' as well     11/29/17

Hey Bob,
Any tips for getting the Nitrate down?
<Ah yes; avoidance from the get go, water changes, biological amelioration, chemical filtrants. Gone over in detail here: http://www.wetwebmedia.com/fwsubwebindex/fwnitrates.htm
and the linked files above>

It's got me beat, the Ammonia reads 0 ppm to 0.25 ppm if that, as I stated previously I do regular water changes, vacuum the substrate but the Nitrate stays up.
Have tried a little bit of Poly-Filter about the size of the Ammonia Test kit box as recommended by the Aquarium place I bought it from.
<A worthy product>
But if the fish (Electric Yellow & leleupi) have laid eggs their got to be happy right?
<That or stressed; either end of the spectrum elicits reproduction, reproductive behavior>
Up until the Black Ghost Knife fish became crook I've had no problems.
<And you, Bob Fenner>
Re: Black Ghost Knifefish     11/30/17

Thanks again, Bob really appreciate your help.
I will have a read of that site you forwarded.
Kind Regards
<Real good mate. BobF>
Re: Black Ghost Knife fish; Nitrates f'      12/2/17

Righto' Bob,
Sorry to annoy you.
<Not an annoyance Gav. We're here to share>
I read the literature on the web site you forwarded, even though it mostly spoke of Marine set ups, it did in parts touch on Fresh water and in part mention the filter system.
That got me thinking do I NOT clean my filter regularly enough? Is the filter the reason my Nitrate/Nitrite is high?
<This is definitely a possibility as source of NO3. Mechanical filter media, accumulating materials that can/do break down into Nitrate is a principal source of this nitrification product>
All most people say is do regular water changes.
I am under the impression don't mess with the filter, clean it when you notice the flow rate drop, say every 6 months.
<Mmm; well; we need to expand on our ideas, terms here. "Filtration" is a very large concept; for instance, it encompasses denitrification, a set of processes "in reverse" that convert Nitrate largely to Nitrogen and Oxygen... under anaerobic conditions. Are you aware of this?>
I use an Aqua Pro 2200 Canister Filter. The 3 sponges & wool in the bottom basket, the rest filled with Biohome Standard Media and a tray of BioBalls which is all suppose to allow for colonisation of bacteria's and alleviate
Nitrate/Nitrite problems with less cleaning time.
<Actually... you may want to investigate a bit more here. I would switch out the Bioballs and if you have more of the Biohome Standard Media or other sintered glass (e.g. Siporax) filter product, use it in the BioBalls space. These balls drive the forward reactions of nitrification too much, too fast. You will likely see a difference on their removal, substitution within a few days>
Should I be cleaning the filter more often? Have I got the filter set up wrong?
<Just the BioBalls part here>
In the tank it's self are two air stones (bubbles/water movement), a sponge filter, an Aquael Turbo Filter 2000 internal filter and I use it with just the sponge like a power head pointed from one corner of the tank to the
width of the tank so no dead spots (2 Ft..) more bubbles/water movement, right? Also an Eheim streamON+5000. Optimum water circulation with a natural, smooth current formation.
As I have stated previously, the fish seem happy, there colour is bright except for one has dulled since I bought him (was red, now more brown) one has completely change to a better colouring, Nice dark blue with a bright
yellow streak from his mouth through his Dorsal fin to his tail (a Hap).
There is lots of water movement and air ration in my tank I think Bob, so is the filter the problem? What do you think?
<Fishes and non-fish aquatic life can become accommodated to higher NO3 concentration over time... but I would still aim for a reasonable number. There are other mechanisms to control; e.g. live plants use, Deep Sand Bed (in the tank or a tied in sump/refugium), ....>
Once again, again thank you for your knowledge/ information.
<Like tools rusting in a basement, only worthwhile if employed eh?>
Kind Regards
<And you Gavin. Do write back if something is unclear, incomplete, or you have further questions. Bob Fenner>
Re: Black Ghost Knife fish; ongoing... NO3   12/6/17

Hello Bob,
I read the literature on the web site you forwarded, even though it mostly spoke of Marine set ups, it did in parts touch on Fresh water and in part mention the filter system.
That got me thinking do I NOT clean my filter regularly enough? Is the filter the reason my Nitrate/Nitrite is high?
<Might be a factor; best to only clean/change out "part" of the filter media at every interval. As an example, if you're using two units of Chemi-Pure let's say, take out the oldest one and leave the less old one, adding a new unit>
All most people say is do regular water changes.
I am under the impression don't mess with the filter, clean it when you notice the flow rate drop, say every 6 months.
<Mmm; no... better more frequently. Like every month for the mechanical media... the chemical should be switched out/some rotated for new about this same interval>
I use an Aqua Pro 2200 Canister Filter. The 3 sponges & wool in the bottom basket, the rest filled with Biohome Standard Media and a tray of Marine BioBalls which is all suppose to allow for colonisation of bacteria's and alleviate Nitrate/Nitrite problems with less cleaning time.
<We had this convo.... I'd remove the BioBalls, use ChemiPure in the space instead>
Should I be cleaning the filter more often? Have I got the filter set up wrong?
<.... Yes>
In the tank itself are two air stones (bubbles/water movement), a sponge filter, an Aquael Turbo Filter 2000 internal filter and I use it with just the sponge like a power head pointed from one corner of the tank to the width of the tank so no dead spots (2 Ft..) more bubbles/water movement, right? Also an Eheim streamON+5000. Optimum water circulation with a natural, smooth current formation.
<Okay; good to have more circulation, and aeration helps... most canister filters are deficient here>
There is lots of water movement and aeration in my tank I think Bob, so is the filter the problem?
<Not a problem, other than the driven nitrification from the bioballs, but could be improved as I've stated>
Once again, again thank you for your knowledge/ information.
Kind Regards
<Welcome. BobF>
Re: Black Ghost Knife fish     12/11/17

Hello Bob,
Thank you again for your advise.
I will try the Chemi-Pure and a more regular cleaning of the filter.
So many people tell you different things, for me it's very confusing.
<Mmm; don't allow it to be. SEEK to understand the underlying science; question opinions>
I will let you know the results. Until then Merry Xmas & Happy New Year Bob.
<And you and yours. BobF>
Kind Regards
Re: Black Ghost Knife fish      1/24/18

G'day Bob,
Just giving you a little feed back about my aquarium as I said I would.
<Ah, thank you>
While waiting for the delivery of the Chemi-Pure I ordered online I shopped around looking for it.
One aquarium shop had a big sale on De-Nitrate and told me it would do the job. So I cleaned the filter, added De-Nitrate to the filter, made a small water change, left the aquarium to settle tested the water.
Ammonia reading = Perfect. Nitrate = SKY HIGH, so I'm thinking you rip off barstaaards.
Chemi-Pure arrives, clean the filter add the Chemi-Pure & leave in the De-nitrate, do another small water change, after a couple of days, Ammonia reading = Perfect. Nitrate = right up there again. So then I take everything
out of the tank, flush it all clean, find buffalo head cichlid eggs in one rock in their area, take out nearly all the water vacuum the substrate , put the tank back together leave it to settle, Ammonia reading = Perfect.
Nitrate = same - NO change high as a kite. THOUGHT BUGGA THIS, took a water sample to a pet store, they tested it for me, guess what? Every thing Ammonia, PH, Nitrate and a fourth thing (can't remember) PERFECT, SHOCKED AND STUNNED, obviously I have a faulty Nitrate kit, although it doesn't expire until 2020. Get this the wife says told ya so..
<Ahh, good that you checked the checker>
All that worry, money wasted, time spent goggling and seeking advise all for nothing, so obviously the Black Ghost Knife fish and a Peacock Cichlid both died (a couple of months apart) with swollen bellies had a Parasite or something happening.
Anyway the aquarium is crystal clear like the fish are suspended in air, I'm a lot more satisfied, I have left the filter media as is:- sponges and wool in the bottom basket, then the Marine home bio balls with De-nitrate in the next basket, then the Bio-home filter media mixed with De-nitrate, in the top basket is the Chemi-Pure also mixed with the De-nitrate, there was a lot it and I still have one bag of it unopened.
<Good; best to rotate one unit out (the older) and replace it w/ new every month or so>
Now I will leave the filter alone for awhile, but I will order some more Chemi-pure ready for when the current lot expires. Eventually the De-nitrate will expire as well.
Have a good one Bob and many thanks.
<Cheers Gavin. Bob Fenner>

Stress from Water Change Worse than having 20ppm Nitrates in new Tank?     10/11/17
Hi Crew,
<Helen et al.>
I'm new to fish-keeping but have done a lot of research and hope I have got my aquarium off to a good start. I cycled it for six weeks using a fishless cycle with fish food for the ammonia source. I have a 20 gallon freshwater tank with two male Dalmatian mollies, 4 female Dalmatian mollies and two female gold mollies. All but one are less than 1 inch in size, so quite young. I know I may need to move them to a bigger tank in the future. They have been in the tank for eight days and I did a 25% water change four days ago and plan on doing one every week.
<A good interval and percentage. Best to store the new water in advance of your weekly changes; do whatever you intend to supplement (add salt/s, alkalinity...) ahead of time>
I have been testing the water everyday using the API water test kit.
Today's readings were: Ammonia:0; Nitrites: 0; Nitrates: 20; PH 7.6. Temp is 78.4F.
I know mollies are particularly sensitive to nitrates, so I would like to do another 25% water change today to get the nitrates down. However, I have also read that all fish are sensitive to changes in water chemistry so I
am wondering what would be most harmful to the fish - having the nitrates at 20ppm or doing a 25% water change.
<You are right to be concerned here. As you hint/state there are trade-offs in doing too frequent/serial dilutions, and just tolerating nitrogenous et al. accumulation>
I would also like to add some aquarium salt to the water but am again hesitant to change the water chemistry too
much when they have only been in the tank for eight days.
<I WOULD go ahead with the salt addition/s... some every day. This will also reduce the Nitrate toxicity>
Your advice is much appreciated!
<And gladly rendered. Bob Fenner>

Nitrate...      10/6/17
For Neale Monks and Bob Fenner
Hello again friends,
I’d appreciate your comments and reasoning about a question involving lowering nitrate. I will start by saying that I understand that nitrate like ammonia and nitrite is toxic to fish, though at much different levels/exposures and depending upon species or age of the fish (fry being more susceptible) [please correct me if I am incorrect here or anywhere else].
<This is correct; though the mechanisms, pathways if you will, for poisoning/toxicity of these nitrogenous compounds are different. NO3 in particular can be accommodated; i.e. much higher concentrations can be tolerated with long exposure>
Consequently, if one discovers nitrate levels in an aquarium are high, say 160 ppm [I am using an actual case from my work on TFF, and this is a stable state not something sudden], immediately reducing the nitrate to safe levels (under 20 ppm) is not in itself going to harm fish.
<Usually; yes>
I have been challenged on this, with the suggestion that the nitrate should be lowered gradually over days or weeks, similar to other adjustments.
<Mmm; no. Immediately lowering NO3 concentration is advised>
The idea apparently is that “old tank syndrome” is dangerous and rapid changes can be fatal; but I would respond that the danger with this is due more to pH, and ammonia being ammonium in acidic water and the sudden change to basic pH (pH shock, plus ammonium converting to ammonia) is the problem, not nitrates decreasing. My argument is that nitrate is not like other adjustments (GH, pH, temperature, or whatever) and being toxic the sooner it is lowered the better.
<I concur>
I maintain that any toxin in the water, be it ammonia, nitrite, very high nitrate, substances released from wood or rock that are detrimentally affecting fish, etc, are best corrected rapidly via significant water changes.
Comments please, with thanks.
Byron Hosking.
<Will ask Neale for his separate response here. Bob Fenner>
Re: For Neale Monks and Bob Fenner: Nitrate         10/7/17

Byron, Bob,
I don’t have any real insight into this. But I do wonder if there are differences between species and when comparing marine with freshwater fish. My point being that generalist freshwater fish are able to handle bigger water chemistry changes than more specialist species (or most marines) given they’d be exposed to such in the wild. For example, the pH of a pond can vary between around 7 to as high as 9 once photosynthesis kicks in and dissolved CO2 is used up.
<A useful point/speculation. I do think there are differences between salt/fresh, young/old, acclimated and not species, specimens. Have been to public aquariums that fed huge amounts of food to very large animals... that had thousands of PPM of NO3>
I’ve read before that the idea we can meaningfully acclimate fish to slight pH changes is actually erroneous anyway. The “float them in a bag for an hour” or “drip water into a bucket for an hour” approaches sound good, but supposedly the actual physiology works far more slowly than this. So for fish to actually adapt their blood chemistry (or whatever) actually takes far longer, and what we’re really dealing with is the degree to which fish can tolerate abrupt changes (i.e., shock) and then slowly adjust across days or weeks. Does this sound familiar to either of you?
<Yes; it does>
I do believe, Byron, that there’s a hierarchy of stress factors, and sometimes to minimise a severe stress (such as nitrite, ammonia or extremes of temperature) you may have to increase a mild stress (such as small pH or hardness changes) simply through doing water changes. Of course the standard advice should remain that water changes need to be made with water as similar to the conditions in the tank as practical.
So far as I know, nitrate toxicity hasn’t really been studied across a wide range of ornamental freshwater fish, but experimentally with things like goldfish you really do need quite high levels (100+ mg/l) to cause immediate health issues. In such situations, I think doing moderate water changes across a few days, rather than one giant water change, might be safer in terms of minimising sudden pH, temperature or hardness changes. But that said, if the new water was similar enough to the old, doing 90% water changes has been demonstrated to be perfectly safe in and of itself.
Anyway, keep me posted with what you learn!
Cheers, Neale
<And you, BobF>
Re: For Neale Monks and Bob Fenner        10/7/17

Thanks Neale and Bob.
So what I take from both of you is that with the proviso that parameters (GH, KH, pH , temperature) are close enough to be called the same, a large water change to reduce nitrate from 160 ppm down to 10 or 20 ppm is not going to harm the fish, and is more advisable than doing smaller changes over weeks. I will assume my understanding is correct unless you say different.
<This is a good summation>
I do appreciate the benefit of your experience and knowledge on these issues.
<Welcome. BobF>
Re: For Neale Monks and Bob Fenner    /Neale        10/7/17

I would 100% agree with this.
Triage of any kind is about balancing the big dangers against the minor stresses.
Cheers, Neale

0 ammonia, 0 nitrites, 160 ppm nitrates during fishless cycle      5/5/16
I am trying to cycle my 10 gallon tank (for a Betta) using the fishless ammonia method. It's been 6 weeks and ammonia and nitrites spiked and the fell to zero.
<Ahh; done>
My questions are: why are the nitrates so high,
do I continue to dose with ammonia (I have stopped)

will the nitrates drop eventually like the ammonia and No3 ?
<Mmm; slowly; yes; but better to either add some live plants... or do a significant water change... half the water, halve the NO3>
I have just done a 90% water change and nitrates are at 40 to 80 ppm. The tank has a HOB filter, a sponge filter with airstone, a heater and a UV sterilizer. The pH is 7.4, the tap water is hard (and 10-20 ppm nitrates).
There are some (3) plants and the roots of a philodendron in the tank. I plan on adding more plants. What do I need to do?
<Really; just be patient; time going by... Monitor/test every few days... NO3 will "go down".>
<Welcome. Bob Fenner>
Re: 0 ammonia, 0 nitrites, 160 ppm nitrates during fishless cycle      5/6/16

Thank you Bob Fenner!, should I be feeding the bacteria with fish food until the nitrates come down (just bought 4 more plants)?
<Yes; but really... "just a pinch" or a single flake or two per day. Takes very little to sustain a nitrifying population>
Thanks again,
<Again welcome. BobF>
Re: 0 ammonia, 0 nitrites, 160 ppm nitrates during fishless cycle      5/6/16

Great, thanks again for the info.
<Cheers Eve. B>

For Neale Monks, Nitrates      1/8/16
Hello Neale, and my best wishes for the New Year to you and yours.
<Thank you.>
I will be emailing separately my observations on the flashing/bacterial issue you helped me resolve (thank you so very much) but now I would like to discuss nitrates a bit if you would be so kind. I have frequently read your advice on keeping nitrates below 20 ppm, and naturally I recommend the same when I respond to members of the forum I am now on. I am being questioned on this, so I would like to understand it better.
<Sure thing.>
First thing to get sorted is the unit being used. The scientific community tends to use NO3 N-n, whereas most hobby test kits use total nitrates. I understand the conversion factor is 4.43, so for example the US EPA limit of 10 ppm allowable nitrate in drinking water which is NO3 N-n would equate to 44.3 ppm NO3 with our test kits. When you are recommending 20ppm as max for nitrates, is this the hobby test kit unit (I assume so)?
<Correct. No point citing something people can't (easily) measure at home.
In fact it doesn't usually matter what numbers you choose to use. Most of the nitrate kits I've seen will have some sort of card with them, and that card will be have on it a scale made up of a few coloured patches. The API one for example has seven coloured patches, from yellow (low) to red-brown (high). So long as you aim to keep nitrates closer to the low end of that scale where sensitive fish are being kept, and certainly below the medium colour/number on that scale, you're laughing. Actually knowing what the numbers are is not important. So for that API kit, yellow or orange are fine, red not good for sensitive species like dwarf cichlids, and red-brown probably too much, long term, for anything, at the very least a triggering factor for algae. Make sense?>
To the nitrates, then. Natural habitat waters of all of our fish (so far as I know) have nitrates so low it would probably be impossible to measure them with our kits.
<More or less, yes.>
In the fish, nitrate will act much like nitrite, making it more difficult for the blood to carry oxygen.
<So they say.>
I have come across studies, admittedly on mainly commercial fish and not ornamental, suggesting nitrate levels of 2 to 4 ppm NO3 N-N would affect the development of fry, and many fish and invertebrates will have difficulty with nitrate at 10 ppm NO3 N-N. This study is here:
You have mentioned cichlids likely being affected at levels above 20 ppm, and on the cichlid site it is suggested that nitrate above this may be the true cause of Malawi Bloat.
<Correct. That said, nitrate is complicated. The lethal level of nitrate for some fish experimented on (in labs) seems to be high, supposedly 100 mg/l or more. On the other hand, scientists have only tested a very few (big) species, farmed trout for example, and often their experiments are shorter term things, like how many of the fish die across, say, a week or a month. We're keeping a hundred different species often for years if not decades, so our experiences (and expectations) are different.>
The above is just so you have an idea of where I am with this issue. I guess at this point, I would be interested very much in your thoughts on this, and any evidence, studies, etc., to support our position [I have certainly taken yours ] on keeping nitrates low.
<It's complex. Nitrate isn't something I worry about too much keeping the sorts of fish I like to keep, such as catfish and freshwater livebearers.
Provided other parameters are good, fast-growing plants keep nitrate levels low enough risk of toxicity isn't an issue, and water changes can be carried out as/when required. But if I was keeping species like Dwarf Cichlids or Mollies (in freshwater) that are known to be sensitive to nitrate, in the sense that high nitrate has been associated with disease (bloat, shimmies, etc.) than I'd make more of an effort to monitor nitrate and pre-empt any high nitrate situations using low stocking, low food input, and frequent water changes. Most freshwater aquarists can, I think,
ignore nitrate unless they're (a) struggling to keep a possibly sensitive species; or (b) dealing with an algae problem.>
As always, looking forward to your wisdom, and with sincere appreciation.
<Hope this helps; by no means an expert! Cheers, Neale.>
Re: For Neale Monks, Nitrates      1/8/16

This is great, thank you Neale. Now I have some follow-up, concerning the effects/symptoms of nitrate on fish.
Many if not all of your answers to questions on PFK where nitrates are mentioned as being high involve lowering to no more than 20 ppm. From this I would assume that the effect of nitrate is much like so many things--a source of stress, weakening the fish, opening up opportunities for more serious problems.
<Correct, so far as I can tell. Nitrate isn't immediately toxic like
ammonia or nitrite. On the other hand, because high nitrate levels often go hand-in-hand with things like overstocking and infrequent water changes, it's hard to pick out any problems nitrate is causing from things like lack of oxygen and background acidification cause by nitrate and phosphate accumulation. Tanks with high nitrate levels tend to be neglected tanks, in the sense that the fish keeper has too many fish in them and does too few water changes. So there can be all sorts of reasons fish in those tanks are stressed, not just the nitrate. Make sense?>
One obvious that I assume would occur would be a shortened lifespan from the stress if nothing else. But are there any signs along the way that nitrate may be causing issues?
<None that I'm aware of, but some diseases have been associated with high nitrate level, such as Hexamita and HITH/HLLE in cichlids.>
A member on the forum today mentioned his fish being "fine" with 80 ppm nitrate (which is way into the red on the API card you mentioned) but his Firemouths remained quite pale, and he wondered if this was due to the nitrates. I would think this likely, do you agree?
<It's certainly a possibility. But I'd also observe that Firemouths are widely kept badly. Though territorial, they're bluffers, not fighters, and do badly with genuine fighting cichlids (pretty much all the Central Americans beyond Rainbow Cichlids) and are really best kept on their own with dissimilar tankmates (catfish, loaches, characins, etc.). They're also sand-sifters, so a tank with gravel would be wrong. Finally, like all cichlids, their colours will become paler if they're exposed to bright light from above and/or below. A dark, shady aquarium is better.>
<Cheers, Neale.>

Balloon belly mollies... Not... NO3 rdg.    1/17/12
I have a 20 gal tank 6 moolies,35gal Eheim filter, I do water change 10% every week. My nitrates are up over 40+.
<Too high by at least twice>
I have used nite zorb,it did nothing, I have a RO/DI system. What can I do about the nitrates? Thanks
<Read: http://www.wetwebmedia.com/FWSubWebIndex/fwnitrates.htm
and the linked files above. Bob Fenner>

Nitrates, FW   3/1/11
I have a 55g setup containing a Black Ghost Knife, an Oscar, and a Plecostomus.
<Far too many fish in very little water, plus the Black Ghost is sensitive to low oxygen concentration, and the Oscar sensitive to nitrate.>
The tank has been running for a little over a year now and the fish are producing more wastes resulting in higher nitrate levels. I do a weekly water chance to bring the nitrates to under 10 ppm but by the next week they are high again. I would ultimately like to get a 125g for these fish
but in my current living and financial state that is not possible.
<Very short term I'd rehome the Pleco -- adds nothing to this system. Algae better cleaned by hand, and all the Pleco does is dump solid waste into the filter, reducing filtration, while cranking out lots of ammonia.>
My short term solution would be to get another filter, maybe a Marineland Emperor because of the bio wheel.
<Won't have any effect on nitrate.>
Would the addition of another filter prevent nitrates from accumulating so much between water changes?
<No. Biological filters *make* nitrate. The amount of nitrate is proportional to the number/size of the fish. To remove nitrate you have three main options: fewer fish, more water changes, and/or less food. Denitrification in aquaria is difficult to do without considerable expense and engineering, and plants, while excellent nitrate removers, aren't going to make much difference in a tank this size/stocking density without very strong lighting and perhaps an external sump with plants in there as well.>
Also, my Plecostomus has hardly grown the entire time I've had him while my Oscar that I bought the same day has gotten huge. I realize the Oscar grows faster and larger but the Pleco hasn't even grown 2 inches in a year.
<Not getting enough of the right foods?>
I was thinking of adding some of the plant food that I use in my 29g planted African tank (Leaf Zone) to stimulate algae growth so the Pleco can have more food available. Thank you for your advice and opinions.
<More algae = more food = more nitrate. Hardly what you want.>
<Hope this helps. Cheers, Neale.> 
Re: Nitrates 3/1/11

Thanks, it does help. I just can't get a large aquarium yet, as much as I'd like to. I had considered rehoming the Pleco. I have 2 pumps in the tank to circulate water and detritus. The Ghost Knife loves hanging out right in front of one of them.
<Yes; they inhabit pools and rapids in the wild, so prefer (need, long term) lots of water current.>
I don't trust the denitrifying chemicals or units plus they are pretty expensive.
Both large fish are almost fully grown so hopefully it won't get much worse. If I got rid of the Pleco I feel I should be okay with weekly water changes.
<Possibly, but 55 gallons is really not much for an Oscar and a BGK; 75 gallons better, but 100+ gallons realistic for long term success.>
They both seem to get along fine given the amount of water that they share.
<Indeed, but they will both grow, and both are prone to slowly developing issues that aren't obvious. Oscars develop Hole-in-the-Head and Hexamita infections when exposed to less than perfect conditions. May takes years for it to become obvious.>
I got them about a week apart and I've never seen them fight. Actually the BGK and Pleco fight more, most likely because they occupy the same space.
<Likely so, and both are territorial.>
Thank you for your insight
<Glad to help. Cheers, Neale.>  

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