nitrite levels

This is largely a matter of opinion, I don't know scientifically what level is damaging, but I wouldn't want any of my fish to be subjected to anything above .5 ppm. I am not experienced with Bio-spira, but my understanding is it has both types of bacteria in it, so as soon as the nitrite starts to show up it should be converted to nitrate. It would be helpful to know fish load( size type, quantity) tank size, water parrimiters etc. Some fish handle nitrite better than others, but it will kill all fish if they are exposed to it for long.