I have a 90 gallon sps dominated tank. Its been setup for about 6 months the only fish i have in there right now is a spotted mandarin. I been having a problem with some corals with polyp extension and i've had some problems stn on some corals and burn't tips on another. I run the elose planet 2 mh fixture. I see different problems with different corals, stn, tip burn, poor polyp extension can this all be caused from low nutrients?