my bronze cory is doing something really weird, he keeps on flicking against the sand too many times for it to be whitespot. i'd say about...twenty flicks in about half a minute or something. none of the other fish are displaying any signs of disease or infection, and he is not showing any whitespots all over him, but he just keep on flicking really fast against the sand...checked my water stats, everything is fine, no ammonia etc. what could the problem be? he is in a 600L tank.