snails, small crabs abd algae grazing fish (tangs, fox, angels, blennies, etc). Other things you can do is make sure your water quality is ok, maybe your ovewrstocked...
Also, I have heard of phosban that removes the phosphates and the algae sufficats, and UV sterilizer seem to also work. Best bet is to check you water & make sure you top off w RODi.
Oh, and if your tank is new, I have heard that this is a natural process it under goes. GL, hope it helps!