Ther are going to move arond until they find a place where they like the flow & lighting. If you have brisk flow, or low lighting, they may move around constantly. For some reason they REALY like to be inside a power head >_<

The only safe bet is to put a sponge filter over the inlet of the powerhead, but then you need to clean it on a regular basis.

Did you put these in your 135, or one of the smaller ones? What's your lighting?