I had two nice size colonies growing together.first I noticed some bleaching then the next day the colony was losing all of its tissue,it looked like slime but was still attached to the skeleton,blew off easily with a waving of my hand.the next day the colony next to it was doing the same.everything else in the tank seems fine.across Millies etc.any thoughts on what would cause this?alk stable at 8,mg 1500, nitrates 2ppm salinity .025