I never use sponges that come with it. I always use poly fill. Cheap, easy. For $5 at walmart i get enough to last a year per filter with HEAVY waste load and requent changes. Bottom 2 trays media and top tray polly fill. Change out poly fill monthly. Throw away then put in new. Sometimes i clean media by using tank water in a bucket as not to kill good bacteria or when feeling lazy just hose it off and neglect water change that week. Everyone has their own technique. Majority my tanks are large central americans and tanks have drift wood and large lava rocks ,etc so it isnt as colossal if i kill bacteria in filter because much in decorations but again never do water change at same time as thorough filter cleaning except when i use tank water to clean canister filter.