Contrary to popular beliefs, nitrite is not very toxic to marine fish. It's much more harmful to freshwater fish. However, you should try to find out the source of the nitrites.
Nitrite and the Reef Aquarium by Randy Holmes-Farley - Reefkeeping.com
"In reality, nitrite probably is not toxic enough to warrant measuring in most marine systems."
"In the only published article
that I could find showing toxicity tests to typical reef aquarium fish, Tom Frakes and Bob Studt exposed tank-raised clownfish to nitrite concentrations ranging from 0 to 330 ppm
in artificial seawater. Two of five fish died after a few days at 330 ppm. At 33 ppm (the next dose down from 330 ppm), the fish were lethargic and breathing with difficulty, but otherwise experienced no lasting problems. At 3.3 ppm nitrite no effects were observed