I have two clams in my tank for three plus months. My crocea sp? opens totally still. My teardrop mantle opens maybe half way for 3 weeks. I see no damage and mouth looks good. They both thrived from the minute i put in tank. No new fish. 70 + soft and hard corals all doing great. Any ideas. Someone said do freshwater drip. Had a limited flatworm problem on one hard coral and a few mushrooms treated conservatively.