Nitrite toxicity at low pH

[dalto]

I used to have a chart that had nitrite toxicity levels at various pH levels. Unfortunately, the site that was hosting it has dissolved.

In trying to research nitrite toxicity there seems to be an abnormally large amount of contradicting information out there. Everything from .25 nitrite will cause long term damage to under 4ppm is harmless at all pH levels.

Is there any good data on this available?

 

[aqua_chem]

Nitrite toxicity should not vary significantly at pH in the range that you would expect to see in freshwater aquariums. Speaking in extremely broad terms, nitrite becomes more toxic at lower pH, but you only start seeing significant effects below 6 and above 8, and even then the literature is conflicting on the matter.

Regarding nitrite toxicity, there are a lot of conflicting opinions out there for sure, but much of that is based on, well, basically nothing. There is a decent amount of literature out there on the matter, but I would summarize as such:

Chloride is a major factor in determining nitrite toxicity.
Calcium and carbonate are significant but not nearly as much as chloride.
Higher levels of oxygen help fish combat nitrite toxicity.
Fish vary greatly from species to species in nitrite toxicity. Salmonids are among the most sensitive, and much of the research as been done on them for their economic importance (ie, it's fundable).
The smallest fish tend to be more resistant to nitrite toxicity.

 

[dalto]

Thanks! That is helpful

Do you have any idea at what level it becomes concerning for typical tropical fish found in freshwater aquaria?

 

[aqua_chem]

You really can't just lump FW fish into a single category like that. Something like a platy could take significant chemical abuse, while something like a ram can take much less. For instance, half of rainbow trout will die at .5 ppm for 24h, while largemouth bass can take 160 ppm. Lower concentrations are need for <24 h. As previously mentioned, chloride levels will have significant contribution to toxicity; 40 ppm increases the 24h 50% lethality of rainbow trout to 10 ppm.

I don't think there's any sound data to suggest a specific 'safe' level of nitrite for tropical freshwater fish other than 'that sounds about right'. Lots of anecdote, little data. I would say no more than 1 ppm for 24h, but that's strictly my opinion.