I have used krylon fusion and another off-brand spray acrylic for items to be placed IN the tank before. My DT has pvc-frame rock columns that were painted with fusion, and it's going on 2 years now without any measurabe deletrious effects. Just be sure you let whatever item you've painted DRY for at least 24 hours before you go putting it in the tank, and honestly the longer you let it dry, the better. I waited 7 days for the frames to dry in my DT, and another set of rock columns that went into another tank got a 3-day drying time. Basically you ant to make sure that any VOC's that might be present in the paint to evaporate off. IMHO Krylon Fusion is very reef-safe.