I have been trying to figure out why several of my different colonies are receeding? So far I have a trumpet, two candy canes, several acan lords and micros that are showing the problem, It also looks like my frogspawn is also doing it. what is happening is the tissue slowly receeds toward the mouth till it totally wipes out the polyp, it isnt a quick process, it takes several weeks and can be hard to notice till you notice more and more white skeloten. on the acans and micros it starts at the outer rim of the colony and works its way in. Im kinda baffled right now, Ive tried more frequent water changes, and all my parameters seem to be in check. The only real changes ive made to my system latley is a Geo Kalk Reactor, I only stir it once a day so I really dont see any changes from it. I have always struggled with calcium and Alk being up but have never had recession before, Just hoping this rings a bell with someone. thanks