clam trouble

[Mike-fish]

my 5" clam (cant remember what kind it is) has been partly closed up for the past 3 days. ive never seen any one nip at it so i doubt its that. all parameters are good except PO4 at 2.5ppm + eeeekkkk not unheard of it was for probably a good month or more after we got it so that as well could be ruled out.