I have a leather coral that has shrank to 1/4 its normal size. Last night everything was fine It still has its polyps extended but the body has shriveled to nothing. The water tests are all ok (nitrate 05 amm 0 nit 0 phos 0 calc. 405 ) The other corals -zooas,xenia crocea clam, and all the fish are doing fine. Any ideas