Do you play with light settings? I had many issues with stn and rtn and they would look great for a week or so then the stn would kick in and rtn would follow. Some of the stn would start at the base and some would start at the tips. I’d also get some kind of brown slime on the tips as well. Anyway, at this time I was using gfo, nopox, bio pellets and I would change the intensity and spectrum all the time. Once I got a par meter I discovered that I had really low par readings. So I got the par up, stopped messing with light settings, and got rid of all of my nutrient export other than my skimmer. Acros look better than ever. They’re finally encrusting.You’re correct. I think I had a Dino outbreak. I have since turned off my skimmer, been feeding more and turned my lights down. In spite of efforts I think my corals are toast
I know this will get some criticism but I also turned my flow way down. I know other sps keepers scream high high flow but I have live sand in my tank. If I held a flash light to the water when the lights were off it looked like little particles were literally sand blasting the Acros.