my filter that i got form pet shop... it has like wool in it that all the dirty stuff get stuck inside... already i have washed it a few time when it become a yucky colour .. like a green or a faded brown..

but i heard people say can replace with a sponge?
what kind of sponge, a special one? or just the one that we using to wash the dishes and kitchen? can i just put this sponge inside it? or what kind of wool is it if i wer to replace it ..

bcoz i think in another week or so the wool will become a permantly stain