[Craig Manoukian]

This is from my good friend and chemist and amplifies the good information boomer posted on Nitrites:

With respect to Nitrite toxicity in salt versus fresh water, honestly in most well established aquariums the point is mute because you typically have the same concentration of ammonia consuming bacteria as nitrite consuming bacteria. Nature abhors a vacuum as a long as there is a nutrient, there is a bug to consume it. That being said there have been significant studies showing decrease methohemoglobin production in fish in fresh water containing small amounts of chlorides. Methohemoglobin is produced in the bloodstream when nitrites are absorbed through fish gills. The nitrite ions reduce the iron from a +3 state (ferric) to a +2 state (ferrous) making the molecule as a whole incapable of oxygen transport. The fish suffocates on a cellular level.

In salt water systems the chloride are very much present and the toxicity of nitrite is much reduced...to a point. When the nitrites get high enough, death is imminent. Fresh water fish don't have the chloride ions and therefore are more susceptible.

E

HTH