I used to have a big problem with red slime algae, but seem to have conquered it with an aggressive treatment. First, I ran some phosphate sponge for a couple of days, replacing it after 24 hours each day. Then I ran some carbon to polish off the water a bit. The last step was to take out all the chemical filtration and add (I was very nervous about doing this even though everyone insists it is safe) a red slime killer. I used No-cya-no by ecolibrium. I got it from that pet place online and had to reorder because I ran out in the middle of a treatment. This seemed to if not eradicate the problem completely, neutralize it so that I can't find any red slime anymore. The other problem could possibly be your lighting cycle (per a lfs) or you may need to replace your bulbs. Anyway, hope this was helpful. By the way, if you do use the red slime remover, it supposedly is biodegradeable and will disappear on its own from your tank, but I would toss the carbon and phosphate sponge back in again anyway.