Tony,
I think after checking everything in the tank, it was heat. I had a very large submersable return pump that was really heating the tank up and reducing the amount of oxygen in the tank. The tank temp was around 90 degrees. Unfortunately I didn't realize this until it was to late(my bad). I've since replaced the return pump with two pumps, one external and one submersable. Eventually I'll replace the submersable. Doing this dropped the temp. 10-12 degrees.