I purchased a bi color angelfish about a week ago, and up until yesterday he seemed to be doing great. He was eating well (spirulina and mysid shrimp) and was getting along well with my other fish (potter's angel, clown fish.) However, starting yesterday he seemed to be less active, and started spending most of his time hiding in the live rock while not moving much. He came out and ate this morning, but immediately went back to his little cave, where again he is just sitting there while not moving much at all. Is this normal or do I have a sick fish on my hands? As for my water parameters, everything looks great except my ph seems to be a bit low (8.0-8.1.) Any advice would be appreciated.