Save your money and don't bother with them. If your undergravel (u.g.) filter is partly gravel vacuumed every week or two, when you do partial water changes, it should do well for the rest of the semester. Do you drive home from school? If so, maybe you can drop the water level in the (those?) tank(s), cover them with plastic wrap, pack them in the back seat for the drive home, and the nitrogen cycle may still work when you get home. (That worked for me, but the drive was only about 75 minutes.)

U.G. tanks should be completely re-set-up every year or so. If not there is a real danger that they will have a funky reaction (can you say biological time bomb?) and do the fish great harm. BUT, while they are relatively clean and unobstructed in their flow, they are the best biological filter for the money, anywhere!

Shedd Aquarium basically pipes their water through four giant sand and gravel filters. Of course each filter is the size of a couple of dorm rooms.

We've been privileged to meet several college students on GL. GuppyLuver15 recently posted a couple of diaries. squack15 is another student who has asked some great questions and, like GL15, offered some neat insights.

I'm also very impressed that your dorm or residence rooms are warm enough to keep fish. My dorms rooms usually were not consistently warm (or were seasonally too warm) to do that. [Of course we had wood stoves back then. ;) ] When I moved off campus, tanks began following me to grad school. Just what every history student should have around the place.

Not all dorms are warm enough this time of the year. My daughter "rescued" a crowntail Betta from Wally-World last fall. It has resided on the glass top of my only heated tank since Thanksgiving. I'll bet it returns with her after spring break. ;)

As for those little cartriges... Toss the plastic cartrige in the recycle and the carbon in the garden. If the cartrige can be opened and the activated carbon replaced, well..., maybe keep them. :)