AC is good HOB(Hang on back)Filter, the #20 is the max size of tank it is desinged to filter, although most people go higher because alot of filter brands think there filter does more then we think it does

.. As for the sponges it functions mechanically to remove suspended dirt particles and other debris from your aquarium. It also encourages some settlement of beneficial bacteria to aid biological filtration. The Bio Max balls are made to support a huge colony of beneficial bacteria. These bacteria are vital to your aquarium's water quality as they help de-toxify highly poisonous substances suck as ammonia which is broken down into nitrites and even more bacteria that breaks that down into nitrates which is the least harmful but still can be in large amounts.. AS for the filter floss it does the same thing a sponge or foam insert does, it basically takes the larger particles of debris out of your water and prevents the bigger particles from reaching the small pores of yor biomax which will slow and eventually clog your filter..