I was getting that red slimey stuff pretty bad a few month back. Especially twards the end of the photoperiod. I have tons of flow, use ro/di, did water changes ect bla bla bla. What finally stopped it was when I redid my rockwork, there was a TON of detritus trapped under my rocks feeding the stuff. I also stuck a few powerheads behind the rockwork to keep the stuff from collecting. I put the powerheads on a timer so once a day at 6pm a big cloud of fish poo erupts from behind my rocks, falls to the sump where it settles and can be easily removed during water changes. Its like flushing the toilet once a day wether you need it or not. O ya, everything in my tank looks much healthier since and I no longer have a nitrate problem. sulpher denitrator for sale soon!!!