# Nitrates Toxic?



## dwalstad (Apr 14, 2006)

Hi Folks,

There have been many recommendations to keep nitrates low (below 25 ppm) in our aquariums. I'm not sure why, because the scientific literature and experts _repeatedly_ imply that nitrates aren't very toxic. At the end of this letter, I have listed documented values from the scientific literature.

What concerns me is that hobbyists are testing and worrying about something not very significant in terms of fish health. One of my tanks runs for long periods with 40-100 ppm nitrates. Meanwhile, hobbyists may be ignoring major toxins like nitrite and ammonia or incorrectly attributing disease problems to fish weakened (?) by nitrates.

The only downside of high nitrate levels is that sometimes they can lead to nitrites in the tank. Nitrite accumulation can occur due to incomplete nitrification or nitrate respiration (a bacterial process promoted by high nitrate levels and anaerobic conditions). I've described how this can happen in my book, pp 65-66. Nitrite, which is very toxic, should be kept below 0.02 ppm.

HOWEVER, the most direct means of monitoring rare potential problems due to high nitrates is simply to test for nitrite.

Finally, remember that scientific papers almost always use the term NO3-N, which can easily mislead hobbyists into thinking nitrates are more toxic than they really are. One NO3-N is equivalent to 4.4 nitrates. So if a scientific paper says guppys die at 200 ppm NO3-N, it means 880 ppm nitrates for hobbyists. I could be wrong here, but I think that most hobbyist testkits express nitrates as NO3, not NO3-Nitrogen?

Recommendations to keep water nitrates low are not a bad idea. We all like to keep our fish in relatively clean water.

But are nitrates toxic? You be the judge. After I finished compiling this data, I wonder why I even bothered testing for nitrates.

Anyway, here is the data:

*Nitrate's Effect on Fish and Invertebrates.​*
Largemouth Bass	420 ppm	None on mortality or growth over a 5 month test

Channel Catfish	420 ppm	None on mortality or growth over a 5 month test

Chinook salmon	5,800 ppm	50% dead in 3 days (96h LC50)

Rainbow trout	6,000 ppm	50% dead in 3 days (96h LC50)

Channel catfish	6,200 ppm	50% dead in 3 days (96h LC50)

Bluegill	1,800-8,800 ppm 50% dead in 3 days (96h LC50)

Guppy	836 ppm 50% dead in 3 days (96h LC50)

American Oysters	11,500 ppm	50% dead in 3 days (96h LC50)

Japanese Oysters	4,400 ppm	No effect on growth

Sturgeon, juveniles	4,400 ppm	50% dead in 3 days (96h LC50)

*Note: I converted documented values (expressed as mg/l of NO3-N) to ppm nitrate (NO3). One mg/l or ppm of NO3-N is equivalent to 4.4 ppm of nitrate. [Most hobbyist test kits measure nitrates, not NO3-N.]

REFERENCES

Hamlin HJ. 2006. Nitrate toxicity in Siberian sturgeon (Acipenser baeri). Aquaculture 253: 688-693.

Russo RC. 1985. Ammonia, nitrite, and nitrate. In: Rand GM and Petrocelli SM (Eds.), Fundamentals of Aquatic Toxicology. Hemisphere Publishing Corp. (Washington, D.C.), pp. 455-471.

Spotte S. 1979. Fish and Invertebrate Culture. Second Ed. Wiley-Interscience Publications (New York).


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## southernflounder (Nov 5, 2006)

Fish I may understand but how about shrimps, especially the expensive CRS that some may have. Since a decent amount of us keep shrimps in our tanks should we not worry about the nitrate for them?


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## BryceM (Nov 6, 2005)

This is good info and is backed up by a large body of research. That said, the majority of these studies have been carefully done with fish in laboratory conditions (bare tanks, continuous water exchange, no active nitrogen cycle, etc). Their results would have been invalidated by the presense of any ammonia or nitrite.

Our tanks are quite different. We have relatively enclosed environments with a huge organic load once the substrate, mulm, plants, inverts, and fish are factored in. Ammonia is constantly produced by the fish and other critters. In an aquarium this can either be removed by the plants directly or through the traditional "nitrogen cycle".

This is the question that still remains: "Is it possible to acheive zero, or near-zero ammonia and nitrite levels _in a typical planted tank_ when nitrate levels are above 40 or 60 ppm?"

I don't know the answer to this, but I suspect that it's easier for a system to handle ammonia and nitrite when nitrate levels are low. DW might be right that nitrates by themselves aren't terribly toxic, but in practical terms, high nitrates in our tanks might be a proxy indicator for other evils. I sure haven't seen an actual planted tank that can function well in the range of 200 ppm, regardless of what these studies show. In my personal experience, I can see detrimental effects in the fish once NO3 levels get above 80 or 90 ppm. Spawning behavior stops and they show much less energy.

BTW, NO3-N is a confusing abbreviation. Most scientific papers report nitrate as nitrogen. Lamotte NO3 kits report nitrogen, which must be multiplied by 4.4 to convert it to NO3. Many others are calibrated to read directly in NO3. Like everything else, it's potentially confusing and you need to be careful of the units.


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## JanS (Apr 14, 2004)

guaiac_boy said:


> This is the question that still remains: "Is it possible to achieve zero, or near-zero ammonia and nitrite levels _in a typical planted tank_ when nitrate levels are above 40 or 60 ppm?"
> 
> I don't know the answer to this, but I suspect that it's easier for a system to handle ammonia and nitrite when nitrate levels are low. DW might be right that nitrates by themselves aren't terribly toxic, but in practical terms, high
> nitrates in our tanks might be a proxy indicator for other evils. I sure haven't seen an actual planted tank that can function well in the range of 200 ppm, regardless of what these studies show. In my personal experience, I can see detrimental effects in the fish once NO3 levels get above 80 or 90 ppm. Spawning behavior stops and they show much less energy.


That's exactly right guaic. I guess I don't know the answer either because I don't let my nitrate levels climb that high, but I never see ammonia or nitrites either once the tank is past the initial cycle.

I don't mean this in a derogatory way Diana, but what is the point you're trying to stress to fish-keepers here?
That it's okay to let your nitrates climb to high levels?
That regular water changes aren't necessary or important?
That it's common to have ammonia and nitrites in an established tank?
I'm just trying to get a grasp on where this is supposed to be leading. 

I realize that the El Natural way is a whole different concept, and many people have great success with it, but there are many more people who don't do it that way, so I don't want people getting confused about two totally different ways of doing things.

I could pull up all kinds of different studies that completely contradict the ones you've posted, but as we all know, studies can vary immensely depending on the circumstances in which they were conducted, so I usually don't rely on them as much as I do from successful, experienced hobbyists. 
I've been keeping fish for over 25 years myself, so I have a pretty good grasp of what is stressful to fish and what keeps them thriving, not just surviving.

I can also tell you that with the regular water changes to keep the nitrates below 20 ppm, and the TDS in check, I've never experienced the problems with sick or diseased fish, except in the q-tank which is the _only_ place you should experience them. 
I do admit that I had one summer a few years ago when we built this house and it was about 6 - 8 weeks that I couldn't do a water change, and I had a bunch of sluggish fish who didn't look all that sick, but they sure weren't flourishing like they usually do. When they got back into nice clean water, bam they were back. 

Anyway, I'm not trying to contradict you Diana, and I do admire you for all of the time that you put into helping other people achieve their goals. 

Like I said, I just don't want to confuse someone just getting into the hobby with the differences in opinions on how we do things.


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## hoppycalif (Apr 7, 2005)

If the aquarium is populated with a good density of growing plants it would take a lot of fish to generate a rising level of nitrates. And, if weekly water changes are done, as we usually do with CO2 injected tanks, the nitrate level can't even approach toxic levels as reported by Diana. That is the message I chose to read in her post.


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## dwalstad (Apr 14, 2006)

JanS said:


> That's exactly right guaic. I guess I don't know the answer either because I don't let my nitrate levels climb that high, but I never see ammonia or nitrites either once the tank is past the initial cycle.
> 
> I don't mean this in a derogatory way Diana, but what is the point you're trying to stress to fish-keepers here?
> That it's okay to let your nitrates climb to high levels?
> ...


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## DataGuru (Mar 11, 2005)

Partly what I take from that data is that there is leeway on nitrAtes. That's good news for me given I'm into keeping goldfish who are nitrAte factories. Even with substantial weekly partial water changes, nitrAtes get up over the magic line (the threshhold for goldies that's often quoted is 40ppm). It's kinda like the 10 gallons per goldie rule... or the with goldies, you gotta move 10 times the gallons in the tank per hour. I haven't seen data on any of it, but everyone passes it on like it's gospel. 

Just to clarify, nitrAtes typically don't build up in natural planted tanks to a large part because instead of the bioflter converting ammonia to nitrAte, it gets converted to plant mass. I think there is also denitrification happening in the soil. 

e.g. NitrAtes were only up to 20ppm in my 125 gallon natural planted tank after 6 months with no partial water changes. Fish and plants appeared happy. No drop in pH over time either.

Note however the numbers Diana posted are kill rates.
I've seen Doc Johnson from Koivet talk about immunosupression from high nitrAtes. and I'd bet there are other undesirable physiological effects from high nitrAtes. It's quite interesting that the 25ppm max for nitrAtes posted earlier in this thread is very very much lower than most of the published numbers Diana posted.


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## Minsc (May 7, 2006)

Very interesting 

A while ago I saw a post (on this forum or another, can't quite remember) that indicated that nitrates produced through the nitrogen cycle in our tanks as being much more toxic than the nitrates we add as fertilizer or are likely used in laboratory settings, ie: KNO3.

Perhaps someone with a background in chemistry could chime in on this?


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## joephys (May 9, 2006)

Just because they aren't toxic doesn't mean that fish really like them. Lab results are fine and dandy, but when push comes to shove, my fish are a lot more active, have better color, and extend their fins much more after I do a big water change.


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## dwalstad (Apr 14, 2006)

Minsc said:


> Very interesting
> 
> A while ago I saw a post that indicated that nitrates produced through the nitrogen cycle in our tanks as being much more toxic than the nitrates we add as fertilizer or are likely used in laboratory settings, ie: KNO3.
> 
> Perhaps someone with a background in chemistry could chime in on this?


It is _amazing_ how these rumors get started. A nitrate (NO3-) is a nitrate no matter how it was produced. The KNO3 fertilizer does come with the potassium cation (K+), but the K+ should not make any difference in terms of toxicity (or non-toxicity) of the nitrate.


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## bharada (Apr 17, 2004)

Regarding inverts, at least for members in my club, 90-100ppm seems to be the magic range when it comes to shrimp mortality for the hardier types (Amano and Cherrys). It's probably a lot lower for Crystals/Bees and Bumblebee.


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## banderbe (Nov 17, 2005)

Aren't Discus very sensitive to elevated nitrates?


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