Ive had these in my tank for a while. Never see them on any corals but read where they could feed on zooxanthalle. I'm on a good stretch where things are doing good but still haven't seen colors that I had in the past. I'm getting ready to move this rock and coral to another tank. I'm thinking everything should get a dip in the process and was looking for suggestions. Here is the best pic I can get... Should I worry about them?