Originally Posted by Fresh2o
How many hours are the lights on? What kind of light fixture is on the tank?
Simply reducing the number of hours the lights are on might be the most effective method for reducing algae.
Would also tackle lighting (while agreeing with above that heavy water changes are needed as that tank sounds over-stocked on goldfish unfortunately). I've thought a uv
unit will help with all algae types but best on floating algae, it won't stop attached algae (maybe, could be wishful thinking, slow it spreading but would be looking elsewhere at rest of tank setup as well).
On my smaller tank, I've taped off all blue lights and half the white light & light is on only 5 hrs a day. That just has algae under control and I still need to clean off brown/green algae every few weeks.