thats correct. I am now trying out a new method on the coiled de-nitrater. The norm was to place the coil in the PVC pipe but i now place the coil outside. I bought a 50m roll of air tubing (come with coil container and tape the entire container black. Leaving inlet and outlet exposed. Filled the PVC pipe to the brim with bio balls. This will solve the limited surface area in PVC pipe when 20m air tubes were to share the same space with bio balls and the air tubing benting when not properly inserted or compressed. I could also increase flowrate as coil length and bio balls have increased. Will revert on ontcome