Oh gosh. Ditto. "Don't change their tanks, go study!" Meh. My grades are good enough, LOL. I'm not one to strive towards the high-end, haha.
I would probably have the impulse to (after taking all the water out with the siphon) put some tap water in, swish it over and over and over, and consider the gravel cleaned - and do it once a month or so. Fill it up with tap water, and just treat the entire tank with the conditioner. Since you're not cycling, no harm will be done.