I have 5 acans in my tank. all 5 have been doing great, but then yesterday I noticed that two of them were recessed. Just checked and they remain recessed. The lighting and flow that they are receiving has not changed and are relatively consistent with the other 3 acans that are doing well. All other corals (SPS and LPS) seemed to be doing well. Should I be concerned. Parameters are great with exception that Mag and Calcium might be a little low. PH 8.2, amonia = 0, nitrite = 0, nitrate, =.02. KH = 220, Calcium 400, magnesium 1300. This was based on parameters checked last night. I have since added calcium and mag, but have not checked it.