GET RID OF THAT ROCK... They remind me of GSP but brown like sympodium they don't grow on a matt like GSP but sprout all over the rock work. Not Aiptasia.
I have the same issue, those are very tough to get rid off, I've kalk pasted , aiptasi x'd etc. Them are some really invasive things, will grown on ANYTHING even on Z's and P's, bubble corals, LPS and SPS. No kidding, They reproduce rather quick. I even to a rock, blow torched it, after a couple weeks, new growth. I've already recieved new base rock to replace the rocks that I have those things growing on. Going to take them out of my tank and probably have them soak in vinegar or muriatic acid or something. :doh: