I have a squamosa clam. Been in the tank about a month. Up until yesterday he would close up with no problems at all. Today he won't. I even tapped the side of it with a turkey baster and nothing. He does however pull his mantle in like he's going to close but just doesn't. He is on the sandbed in my 30 gallon. 250 watt MH right above him. I just dosed some B-Ionic this morning. Last time I checked like a week ago it was at 3 meg/l and the cal was at 480. Nothing ever bothers him, no snails on him. Is this normal?