I have a deresa clam that is about 5 inches high for 2 months, my first clam, in a 125 gal reef tank with corals and tangs. Last Wednesday I noticed that it was drawing the mantel in and my purple tank and yellow eye tang were picking at it. I have moved it 3 times and they still seem to pick at it as soon as it starts to come back out and then it snaps shut. There doesn't seem to be anything wrong with it, but I know sometimes fish pick on something if it is sick. I have not done anything different with the tank. I have had my tank for 3 years. I love my clam and don't know what to do. I checked the water and it is perfect. Everything else is growing and multiplying so I don't know the cause. Please help. Thanks Sendie