You cannot over skim a tank. There are corals that do better in less than perfectly clean water though. SPS and most LPS are not one of them.
Correct calcium/alkalinity/ph
Proper flow for the coral in question, might have to experiment
Very low phosphates (under .05 for SPS)
Proper lighting for the coral in question, might have to experiment
Proper placement with other corals that could be toxic when mixed, watch for stinging or other signs that adjacent corals are fighting back.