We need some general information from you in order to help. What size tank, how long has it been set up, what kind of lighting and filtration, how often do you do water changes, what additives if any are you using, what kind of water do you use (ro/di?) What tests have you run and what are the measurements on them, what kind of fish, how many of each, how long have you had them, what are your salinity, ph, nitrites, nitrates, calcium, hardness, ammonia, etc. Then we can begin to help you with your problem...