The tank has been incredibly cloudy lately, so it's pretty difficult to see in it. I've been doing pretty frequent water changes, but haven't managed to control it as well as I would have liked. Also, spooky fish (the chinese algae eater) has been really busy in the gravel lately. I thought those events were unrelated, until I made an (as yet unconfirmed) conjecture as to what spooky fish was doing. See, there is this pagoda in the tank (more like a landscape) that takes up most of the floor of the tank. It collects lots of decaying crap and such, which causes bacterial blooms. Bacterial blooms cloud water. Algae eaters like to hide in dark secluded spaces (I had two in my old tank that were constantly underneath the plastic log in the tank. They'd constantly burrow underneath it. Ergo, spooky fish is burrowing under the pagoda, and stirring up the decaying crap which is causing the bacterial blooms.
So, either I get rid of the pagoda in favor of some other place for spooky fish to hide, or I clean out under the pagoda every time I do a water change.
Gotta love mother nature.