The other thing to consider, and I'm probably going to end up contradicting myself, is how far along you are in your fish plan. For example, I now have 22 fish in my 265 (on the way to 35 or so) and am far more risk averse than I would be if I only had 5 fish. For Tangs I now treat even in the absence of symptoms, both for worms and skin parasites. Wrasses get treated for worms. Anthias, for now, just observed.