Just FYI, the requirments to keep flatworms alive are about the same for any invertabrate in a reef system. Reducing nutrient input may help some but not as much as you would think. If they are in plaque proportions and covering the corals or anything, get one of those headshield type slugs that eat only flatworms. You'd have to find another home for the thing once it erradicates them, but since that is all they eat, they'll definatly get em down.