I have had a crocea for at least 3 years. It is beautiful. With in the last week to 2 weeks it has closed up. I know it is alive because it still reacts to me putting my hands over the light. I have two other clams, deresa's, that are open and look fine. Only fish in the tank are a bi color angel and maroon clown which have been in the tank forever. Parameters are good. Any suggestions why it is not opening?