I noticed my Heater is losing the black covering but otherwise the tank seems ok. Except my zoanthids are closed up. Could the heater be causing tank issues? The white areas were black before...
Better safe then sorry.. I'd replace it with another heater.
FWIW, I recently purchased a HMO-100 FINNEX HEATER for my coral QT and this thing stays so consistent in temperature. I did the 100W for $35 off BRS.
If you are doing it for your main display, I'd purchase two undersized heaters. That way if one fails on, it doesn't cook the tank and if one dies, the temp doesn't drop insanely low.