2 T5HO is High light on a 55 Gallon and needs pressurized Co2. Either cut back on lights and only run one bulb, add some window screen or raise your lights about 10-12" above your tank. You could also choose to keep the lights as they are and get pressurized CO2. Lots of options, but your current set up needs modified. Also check your dosing as others previously mentioned and do your weekly water changes 40-50%.