So one of my Nerite snails from ReefCleaners came with several small white plaques on his shell. They are just a few millimeters across, flat, and circular or wide oval in shape. Now it looks as if these plaques are reproducing and attaching to my powerhead and skimmer. Any ideas as to what they are? I'll try to post some pics if I can, although it's kinda hard since they are so small.