Something In The Back Of The Filter?

[PiMpPiStOl]

when i got my tank, it came with filter, light, all that. kinda. but my filter didnt come with lil sponges or anything. its a double, with 2 sides that pour out. i have those 2 blue filter thingys, but do i need a sponge in the back of mine?? when my friend got his, it came with the sponge, but no blue filter thing. hes not using it cuz it doesnt fit back there.. but i was just wondering cuz i think i saw someone say something that made me think that maybe your supposed tohave something back there to keep the bacteria and stuff out. if so, what house hold stuff can i use??