water params should be kept normal(i.e., NH3=0,NO3=0,NO2=40ppm or less), high ammonia will kill the little guys quick. they can usually sustain pretty good in all types of water cloudy, dirty, still, or moving(they will spend most of there time not in the current though)a simple way to tell if u are having water troubles is to jus' "Watch". They will all start heading to the top of the tank(water line mainly). what are the parameters? what is the size of the tank, what else do u have in it? if u find your water to be extremely harmful(as it might be considering u killed 2 already) u should do atleast a 30%pwc. also is the tank cycled? how long have u had it?