maybe you have monti eating flatworms like i did :hilarious it took me a while to figure out why mmy 20+ frags were dieing while my acros were doin great. I not have like 1/2 of a 2-3" frag of purple digitata (but at least i got all of them for free from a fellow reefer getting out of the hobby. but it would have been sweet to still have them. I think that is where they came form but im not sure). anyways, they are SUPER tiny. I had thought they were just debris or detritus. They look like the zoo eating ones, only they are white (the color of the dead skeleton they jsut ate) and about 1-2 mm long!! Anyways, they are super hard to spot and it took me a while to realize it. However, some phosban may help, suposedly lowering nutrients would do it.