No offense, but there's little we can do with "water parameters are OK". You'll want to post some details, such as how long the tank's been up and running, and a complete water chemistry profile with salinity, temperature, ammonia, and nitrate concentrations. Since you've corals, Ca, alkalinity and magnesium test results would also help us help you.
Husbandry practices are also good information, such as frequency of water changes, dosing of calcium and alkalinity additives if used, feeding frequency and with what, etc...