After checking the usual, Salinity, Nitrate and Phosphates. You should be checking Magnesium, Alkalinity and Calcium. These three parameters are very important when keeping short polyp stony,and long polyp stony hard corals, SPS and LPS respectively.
So what effects will low magnesium have on your reef aquarium?
You will find it very difficult to maintain high alkalinity and calcium levels if magnesium is low.
Corals will slow in growth and will cause some corals such as Duncans and torch corals to recede, and in some cases die. You may as many other reefers do, think you have something unseen and/or unheard of eating your corals, because branching heads or receding one by one. Don't get fooled by this, it more likely be the cas…