Hello aem80,
IMO, i think the lights should not be switch on for 24/7 like wat fireblade has pointed out. Plants have biological "sleeping" photoperiod as well. Algae growth can be due to many reasons e.g. imbalance of nutrients (K, N, P, Mg etc...), lightings etc... Generally, moss can survive under low light condition, but prefers cooler waters (it also varies across different species of moss).
BTW, are u refering to the 1.5 ft moss set up in ur gallery?
Cheers!