This acro Ive had for a while now, and as you can see is very established but recently in a few spots its got this problem. I am not sure why it seems that all things are in check as far a parameters. It doesnt look like tissue necrosis of any kind ive seen or like bleaching. It appears like white grains ontop of the tissue possibly being escreated from the coral. I underlined the problem spot in the picture but cant tell what is wrong, any help. Sorry for the bad picture and description