The only thing that worked for me was using a product called Chemiclean, which is specifically for red slime. This may be some kind of antibacterial, although I am not sure. It did not seem to affect anything else in my tank (just had to remove carbon) although this tank was softies only, mostly just zoos. I had great results using this product, but eventually the slime came back (I think it was reintroduced through a frag). I treated the tank again, and since then I have had no red slime (about 3 years). The stuff definitely works, and is worth the price, but I would recommend a non-chemical approach first, if possible.