With absolutely no information about your tank it is impossible to even guess what the problem might be.
We Need (at a minimum):
tank size
age of system
amount of Live Rock
lighting
reactors
skimmer
sump
use of ro/di water
actual water parameters
(salinity, Ammonia, Nitrite, Nitrate, Calcium, Alkalinity, Magnesium - and numbers, not "They're all good")
other inhabitants
and a picture or two would help as well