I currently have a Rena XP2 as my main filter on my 55G tank. Due to the setup of the tank, I don't really have any room for a HOB style filter nor do I have room for another large canister like filter. I'd like to have a diatom filter though to polish my water up a little bit and kill off some of the little bacteria in my tank. Is it possible to use diatom powder with a specific type of bag and have my XP2 function as a diatom filter? Or will I need to buy a completely separate unit?