Join Date: Oct 2008
Location: Baltimore, Maryland
I just re-read your post, and maybe I'm misunderstanding what you're asking. Are you asking if you can remove both a single ballast and its associated bulb from the fixture- ending up with two bulbs and two ballasts? If so- yes.
If the 3 ballasts all share a common (single) power cord, just remove a ballast/bulb at the point where the hot/common (+/-) leads feed it, while leaving the other two bulb/ballasts intact. Be sure to use a wire nut (grommet) on any cut wire ends (electrical tape isn't safe enough). Also, Be sure to keep any grounding wires and connections!
Use a GFCI outlet if you can, but I gather you're in a dorm room, so use a GFCI power strip to plug all your aquarium associated gear into. That's good advice for anyone, really.