What did you do to solve it? Was it only on a single frag or in your entire system? I’ve never been able to keep a healthy monti cap and I’ve tried maybe 10 frags over the past 2 years. Same with acros, although I haven’t tried many of those since I know they’re harder than montis and I can’t even keep those.Nudis maybe? Or red bugs I’ve had a similar issue when I tried adding a montipora same thing happen and I saw red bugs all over it but by that time I realized it was too late, not sure if they can kill them that fast though