Hello to all. I am a long time aquarist, over 50 years. I currently have 2 55 gallon tanks. One has a 10 year old oscar with a Fluval 304 canister filter which is great. A lot of room for different filter media. My other tank is a community tank with an under gravel filter with 2 power heads which I also like very much. My question is are there any products that can be inserted in the uplift tubes that can contain charcoal or ammonia remover and then the power head installed without reducing the flow very much? What about attaching it to the output of the power head? I am talking about some kind of refillable cartridge.