But in the low recommended doses, it makes no difference to nitrate or nitrite. The dosage to deal with nitrite in emergencies it significantly higher. It's also used when shipping fish long distances to reduce the toxicity of the nitrogenous compounds, but again in higher doses.
I'm not even sure it makes any actual difference to nitrate or nitrite in higher doses, I tried it once and it didn't do anything - but then I was using a freshwater test kit.
From what I understand, it lowers the toxicity of these compounds rather than getting rid of the compounds themselves, but I've not really found very much on this subject.
Either way if you need to add aquarium salt to help with nitrite/nitrate, then there is something wrong with your tank.
Short term in emergencies higher dosages are useful, but at the low dosages people add to their tank, it wont help anyway

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using the link above i have some fish the would like a little salt - mollies and platies - but my other fish will not like it. so i won't add yet, still a little confusing......lol
Platies don't need salt at all (but have a relatively high tolerance compared to your other fish), mollies generally do IMO, because without it they can become susceptible to diseases and whatnot.
The thing is that for the salt to actually make a difference to your mollies, you would need higher dosages, and higher dosages would harm your other fish....
Personally, to avoid any trouble in the future, I would take the mollies back and swap them for something similar like sword tails or more platys.
But having said that, if you have become attached to them you can try it. I know that lots of people can ave success with mollies in pure freshwater as long as the water is hard and alkaline (the opposite of what your non-livebearing fish like, but they can adapt better).
Do you know your water stats? If they are below 6.5 (or even 7 sometimes) the mollies you buy in storesare basically impossible to keep alive long term

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