slime buildup.

Ok, so I'm wasting a ton of nutes. I keep having a sludge build up. I'm running a 20 gal. Rdwc with two 5 gal buckets, one airstone in each bucket, submersable pump, and a tote for the main res. I have no light leakes, water temps between 60 and 73 lights off and on. Ph well within range. After...