Some of my zoas have started closing up. My Tubbs Blue was up tp to 20 polyps. It has been closed up tight for a month or so. Now others are closing. My Tyree Toadstool is struggling. I'm over due for a water change. Do you think that's the problem? What else would cause it? Don't see any pests of any kind. Salinity is good, along with alk. Any suggestions?