Another big source of red slime/cyanobacteria is tap water. Too much metal/minerals in the water. Test for Phosphates and also nitrates. If either is high than you need to do water changes. I have had two outbreaks in the last few years and they were due to tap water. I also recommend turning off the actinics for a few weeks. You can also try to increase water flow in the tank. I have a 55 with a 30 gallon fuge and have about 1200 gph going through the main tank. You can get away with just turning the lights off for a few more hours but it will not really identify the source of the problem. Do the tests and see if you have high numbers. I also picked up a test kit from Home Depot to test my water for any metals, nitrates, nitrites ten bucks. Good luck. Also do a search for red slime algae.
Themadd1