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.
Step 1: The Discard-A-Filter
I recommend doing this modification before using the filter (as opposed to using the filter for a few weeks and then disassembling it when you're ready to replace the contents). I bought a two-pack of these and the first one I modded without a hitch, but the second one I had been using in the bowl and it made the plastic too fragile so it started breaking in places I didn't want it to (and not breaking in places I did want it to).
Step 2: Disassembling the Discard-A-Filter
First, remove the clear plastic grate from the top. The easiest way to do this is to start at the top and use a utility knife to cut away the glue that's holding it in place.
Dump out the carbon/zeolite and remove sponge.
Pull out the blue plastic grate. When I did this on the first one it popped out no problem, but when I tried it with the wet one, it broke off.
Step 3: The Modifications
On the back of the filter is a clear tube attached to a blue square which is glued into the back. You'll want to remove this piece. Your best bet is twisting it out with a pair of pliers.
I left the top suction cup in place, and pulled out the bottom one. To block the hole left by the bottom where we pulled out the air hose, I cut the cup part off of one of the suction cups and plugged it back in.
Pull your air hose through the top hole and attach an air stone to the end. The air stone will make your bowl virtually silent, whereas without it, it will be quite loud.
Cut out the bottom 6 or 7 grate pieces, just enough space to allow the air stone to poke through. Now that you've done this the hole blue part will fit back in place the way it was before.
Step 4: Recharging the Filter
Place the sponge back in place. The sponge holds good bacteria that converts ammonia to nitrites to nitrates. If it gets filled with large debris, you might try just swishing it in some dechlorinated tap water to get the larger bits out and then putting it back in. It should last you a while, after which you can just pick up some filter media in bulk to replace it with but doing this may "recycle" your tank (get rid of most of the good bacteria) so you may want to plan accordingly.
Refill the carbon and zeolite into the top portion.
Replace the clear plastic grate on top and fix it to the body with something. The original instructable suggested rubber bands, I used a long sandwich bag tie.
Rinse the filter out under in some clean water to clear out the carbon dust and you're all done!