I'm using a 300l/h trickling filter consisting of 4 round chambers in vertical alignment with 11cm diameter, 5cm height and 5cm distance for the trickling (100 to 500 holes per level) in a 15cm pipe. The top is open in order to allow air exchange. 2 chambers are filled with 2 to 4mm gravel, one with filter cotton and one with clay pipes. It is used for nitrification of aquarium water.
The filter is loud and I want to muffle it. I already figured out that laying 2 levels of microfiber towel on top of it helps. I also have the option to build a wooden enclosure.
What measures should I take in order to reduce the available oxygen for the nitrifying bacteria as few as possible? Could the exchange through the towels be sufficient? Should I use a special membrane in the enclosure? Does it make sense to connect an aquarium air pump to the inside of the filter?