I just purchases a 5" Tridacna maxima Super Ultra Clam. The question I have is I have placed the clam in my sand bed about 18" -20" below my 250watt MH and VHO's... The clam has been in my tank 1 day. How far is the mantel suppose to open on the Tridacna? What does the clam depend on when it comes to opening up fully? ALl my perameters are awesome? Any suggestions would help greatly