The issue you have is... first your lighting is not the best for coraline algea growth, and I am thinking your bulbs arent the right type either. You need to have a better bulb in general than your current set up to stimulate photosynthesis in your tank. I am also guessing that your salinity is lower than it should be for a reef system, mainly because you have a FOWLR system. Low salinity would result in low calcium, insufficient lighting along with your salinity is going to slow down your coraline algea growth a lot.