It is a lot of light and a lot of discus for a 55 gallon. You really do need to work on the CO2, cleaning out all of the existing BBA, making sure there is good water circulation, and, stop fearing phosphate. You need to dose it if you want good plant growth, and without good plant growth, and with all of the discus dumping in the tank, the ammonia spikes will start algae over and over.