I also have that discoloration in my tank, but I am on my way of curing a bad case of red slime that was way out of control. I would clean out the red slime out of my tank by means of turkey baster and net. It got so bad that it would bloom two days after I cleaned it all up. After small water changes every other week and slowed down the feeding the problem is becoming manageable. I am even seeing the substrate recovery. I also am vacuuming the substrate when I do water changes.


Good Luck!