Hi, fishlane! Welcome to AA!!
First off, when you say high nitrites, what numbers are you talking about? Also, it would be helpful to know your ammonia and nitrate readings too.
Are you currently cycling the tank? If so, it's normal to see a nitrite spike as the bacteria that convert nitrite to nitrate colonize the tank. Like Allivymar said, water changes are in order if the nitrite levels remain elevated.
Finally, do any fish appear to be gasping for breath? Nitrite poisons fish the same way carbon dioxide poisons us, by blocking the transport of oxygen to body tissues via the blood.
I didn't know about the salt trick for treating acute nitrite poisoning - thanx, Alli!