Red algae is caused by high nitrates - they feed off it.
Feed fish less
Multiple water changes but this won't fix the problem long term. You need to figure out the source of the nitrates.
Better skimming can help.
Cleaning filters at least once a week.
What type of lighting do you have? As bulbs get older they are not as effective - changing the bulbs can help.
Goober, I have the same problem as you now. My readings are all perfect, and red algae. I do now about water changes every 3 days, to get rid of that stupid red algae. Any ideas of how to get rid of it?