My 55 gal tank was running without any problems except for my nitrates where around 20ppm right before my weekly water change. I wanted to reduce my nitrates and on advice from my LFS I added some substrate (crushed coral) to deepen my bed. I read many articles on sandbeds and denitrifying bacteria, but was unsure if a deeper bed would work with crushed coral. My LFS assured me that it would. After deepening my crushed coral bed, my nitrates reduced to zero, my ph went up (finally coming back down to 8.4), but red algae hasn't stopped growing on my substrate. I'm getting very frustrated and tired of battling it. It's been at least a few months now. Any help, suggestions, or advice would be greatly appreciated.