At what level is Nitrate harmful to fish

[HankstankXXL750 Verified Sponsor]

I can’t find it now, but remember in the past that I read nitrate is not really toxic to saltwater fish, but that long term exposure to high levels damages internal organs shortening the life span of the fish.
Is this a valid statement and if so at what levels.

 

[Randy Holmes-Farley Verified Community Expert]

I do not have a clear picture of what levels are Ok and what levels are somewhat stressful, only what levels actually kill fish, which are very high.

IMO, there are a lot of opinions on what levels are OK and what levels are not, but most are not backed up by clear supporting evidence.

As to death, here's my commentary from a thread related to Seachem Prime's claim to help with nitrate deaths:

How much needs to be present?

Here's from my most recent nitrate article:

Fish, it seems, are not very sensitive to nitrate. Most researchers find little toxicity13. One group that studied a variety of species of fish larvae report:

“Judging from its effect on 1st-feeding, unionized NH3 is a potential hazard in the rearing tank; NO2– and NO3– are nontoxic at levels likely encountered in practical marine fish culture.”14

Here's a post from a professor who looked into nitrate toxicity:

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Maybe it's an accepted belief, but it's not close to being correct scientifically. And there are a LOT of papers on nitrate toxicity in saltwater from just a quick pubmed search.

The lowest LC-50 I could find for nitrate toxicity in a marine environment (for fish) was over 500 mg NO3-N / L. That is about 2200 ppm NO3.

 

[HankstankXXL750 Verified Sponsor]

I do not have a clear picture of what levels are Ok and what levels are somewhat stressful, only what levels actually kill fish, which are very high.

IMO, there are a lot of opinions on what levels are OK and what levels are not, but most are not backed up by clear supporting evidence.

As to death, here's my commentary from a thread related to Seachem Prime's claim to help with nitrate deaths:

How much needs to be present?

Here's from my most recent nitrate article:

Fish, it seems, are not very sensitive to nitrate. Most researchers find little toxicity13. One group that studied a variety of species of fish larvae report:

“Judging from its effect on 1st-feeding, unionized NH3 is a potential hazard in the rearing tank; NO2– and NO3– are nontoxic at levels likely encountered in practical marine fish culture.”14

Here's a post from a professor who looked into nitrate toxicity:

Reef Central Online Community - View Single Post - Can High Nitrates Hurt Health of Fish in FOWLR?

Reef Central is dedicated to the marine reef aquarium hobby. Learn about reef aquarium setup and maintenance, and view coral and marine fish photos. Visit our online community and discuss and chat with hobbyists of all levels from beginner to advanced.

www.reefcentral.com

Maybe it's an accepted belief, but it's not close to being correct scientifically. And there are a LOT of papers on nitrate toxicity in saltwater from just a quick pubmed search.

The lowest LC-50 I could find for nitrate toxicity in a marine environment (for fish) was over 500 mg NO3-N / L. That is about 2200 ppm NO3.

I had read yours, maybe I was wrong, but I thought it was you, but possibly @Jay Hemdal whi made a statement in one of my threads that although not particularly toxic, but causes damage at long term exposure to higher levels?

 

[Randy Holmes-Farley Verified Community Expert]

I had read yours, maybe I was wrong, but I thought it was you, but possibly @Jay Hemdal whi made a statement in one of my threads that although not particularly toxic, but causes damage at long term exposure to higher levels?

That may be true, but it wasn't me who said it. I know lots of people make that claim.

 

[Jay Hemdal Verified Community Expert]

That may be true, but it wasn't me who said it. I know lots of people make that claim.

I typically make two comments about nitrate: 1) be sure people know the difference between measuring nitrate-N and nitrate ion. 2) that nitrate is virtually non-toxic to marine fish at levels really ever seen in aquariums - EXCEPT that nitrate can serve as an easily measured marker for other compounds in old seawater that cannot be as easily measured - phenols, cresols, gelbstoff, etc, and those could be potentially an issue. In addition, old seawater can also have depleted elements like iodine (leading to the idea that high nitrates causes goiter). Spiking seawater with just nitrate, and not having those ancillary compounds in the water seems to show it as essentially non toxic to marine fish, just like nitrite is….IMO.

Jay

 

[Bucs20fan]

I was in a bit of a disagreement with another well known member on this site about nitrates and what levels fish can live in. My fowlr tank has what would be considered by some as very high nitrates. It rarely goes below 50-60 and has been as high as maxing out my hanna checker at 75ppm. I have triggers, puffers, grouper, bamboo shark all in this tank together and have had no issues whatsoever.