hmmm i'm a little concerned that you see any nitrite levels at all. Nitrite is one of the more toxic left overs from waste. You mentioned your tank is 3-4 months old. Tell us a little about your cycle. How long it took, how you cycled it and what the readings were (as you best remember).
Also, tell us how you acclimated these new fish to the tank.
((I'm going to move this to the SW
Sick-Fish forum to get a little more exposure for you))