What kind of filter is it, Silver?
I currently run a Penguin on my main tank, and use their filter cartridge in conjunction with a "homemade" one.
For the homemade part, usually I use polyester batting (aka quilt stuffing) from a hobby shop. I estimate I can "make" about ... 30-50 "cartridges" for around $4 using batting. Three cautions going this route, though:
1) You want the label to say "100% polyester batting". No cotton, no treatments, no dyes.
2) I find it helps a lot to swish the batting in old tank water before installing it. Some of the material tends to 'flake off' when it first gets wet.
3) In my experience, it breaks down more quickly than, say, the fiber material of commercial cartridges. But, it's still usually good for at least a month.
Check
this link to see how to "renovate" a Penguin cartridge using batting, for a very small fraction of the cost of a commercial cartridge.
I've also used sponges (such as the filters they make for AquaClears, but cut to size.). They seem to work pretty well, too.
Also, as far as I know, charcoal is (for practical purposes) merely a chemical filter. It won't help remove "floating gunk" much. (Plus, the charcoal in the media cartridges gets rendered next to useless fairly quickly). Personally, I never use it except for "mopping up" medications.
Since you've just finished medicating, I'd recommend getting a cartridge (or a bag, or whatever) with activated charcoal, and let that run for two to four days, then remove it. It'll remove most of the residual medication.