The idea here is to purchase a cheap disposable filter (around $3 or $4) and reuse it by recharging the carbon and zeolite yourself. This is much cheaper then buying a new disposable filter each time you need a new one. Note that these filters are recommended for small aquariums or fish bowls, so you won't want to use this on your big 55 gallon tank.
Things you'll need:
- Disposable filter (at most pet stores for around $3)
- Air pump, the smaller the better. Mine was only about $5 at the pet shop
- Air stones - these make the thing way quiter. I think it was $1.99 for a two pack and these will have to be replaced every so often.
- Activated carbon, this is about $3 or $4 for a big container of it at the pet store.