Nitrogenous waste.

I have been reading conflicting info on the toxicity of ammonia, nitrite, and nitrate depending on ph and salinity.

Is ammonia more dangerous to fish in freshwater or salt? If so why?
Is nitrite more dangerous to fish in freshwater or salt? If so why? (I have seen posts where Spinycheek stated that nitrite isnt dangerous to sw fish).
The big one. I have read that nitrate is harmless to freshwater fish even with relatively high concentrations, but is toxic to sw fish under the same concentrations.

I know as ph rises ammonia becomes more toxic, is this true of nitrite and nitrate as well?

Alot of the info regarding this topic is contradictory. I have read that nitrates are more toxic in salt water with normal reef ph and hardness. I have also read that nitrates are more toxic in fresh acidic water.

For now we can keep these questions in regard to fish, and not inverts.

wow eddie........great questions.........I am NOT educated much about that chemistry though so I can't really help out..........but I do know that we have a lot of geeks here who CAN answer that for 'ya!

while I'm doing some of my own research on these questions, can some of you chemistry geeks help with them now?

Ok, nitrate (NO3) is chemically the same in both salt and freshwater, it's a pretty stable molecule. My understanding is that the difference in toxicity is primarily due to the fact that saltwater fish, first off are typically just more sensitive to environmental conditions than freshwater fish and because salties ingest water constantly to replenish water lost due to the salt, they inherently ingest nitrate. Now, when nitrate is in the gut, it is converted to nitrite and absorbed into the blood where it converts hemoglobin to methemoglobin which can't carry oxygen. So high concentrations of nitrate in saltwater can cause blood disease.

Nitrite (NO2) is also stable, but it's toxicity is dependent on chloride being present. I do not know what the chemical reaction is, but chloride prevents the nitrite from being absorbed across the gills. So because saltwater is loaded with chloride ions, nitrite is rendered unabsorbable. Freshwater does not have this luxury and is why adding salt to freshwater aquariums helps the fish so much. Nitrite is very toxic because of the hemoglobin conversion, but chloride blocks it.

Ammonia exists in two states, the protonated ion (NH4+) and the standard state (NH3). The standard state is actually a gas that is dissolved in water and can be removed with vigorous aeration. It is also the toxic form. It irritates gill membranes causing excessive mucous production and damages the tissue making gills clump together, it kills by asphyxiation. Now the protonated (NH4+) is created when there is a high concentration of free H+ ions (meaning low or acidic pH). So high pH means ammonia will be in the standard, toxic form, but low pH around 5-6 and ammonia is virtually non-toxic no matter how much is in there.

Thank you Spiny. You are a genius as usual. Now. What effects do the 3 have on inverts?

Why do 10-30 ppm nitrates feed softies, but harm sps?

Crustacean data? lol

Thanks man!

Inverts are more of a mystery to me. They are so diverse with such different physiology, I don't think one can make a blanket statement about how inverts will react. Crustacean's gills seem to largely be affected by ammonia the same way fish are. But they possess totally different "blood", so I really don't know what nitrite does to them.

I do know that with corals, one of the big reasons nutrients are a problem is that bacteria on the surface of the coral grow out of control and create hypoxic conditions on the coral's tissue and kills it slowly that way. This info was found relating to sps, so maybe softies don't have the same kind of bacterial problem.

Spiny.....you need to write a book dude. Your knowledge base is unreal. Great info!

I guess the bacterial growth is one of the resaons sps needs high flow.