I picked up some mussel, clam, and snail shells while I was out at the beach today getting some crabs. (Beautiful day! The water was perfect for wading!) I put them in the tank at first (#3 pounced on the mussel, I think he thought it was more food. He's been eating a lot lately.), but I took them out this evening 'cause I didn't want to contaminate the tank. Is there anything I have to do to clean them? Or can I just leave them in the tank?