I had the same problem that you are describing and that is what led me to pull the false back apart. The tray under the filter was siliconed in and a pain to remove. I thought I broke it when it finally came off. It was amazing what kind of nasty gunk came out of the bottom in the back. After I cleaned the back bottom and kept up with the cleaning about once a month the nitrates were kept in control. I also did about a 5gln water change each week when I had my BC29. Don't forget to pull the pump out and clean it well also - it was a trap for the gunk that made it by the bioball chamber.