I'd completely forgotten about the two black Corys I'd put in the 10-gallon holding tank - the black substrate and thick algae coating on the sides made them nearly invisible. I'd assumed they'd long since perished, to be honest. I hadn't seen many scuds lately, but still fed them, just in case.
Today, I swapped out one of my lucky bamboo towers from another tank, where it was submerged, for this one, where it'll be emergent. I've got some mutt feeder guppies in there too. As I put the tower in, I saw some movement - turns out my two black Corys are alive and well, and pretty plump, at that. I'm guessing they've been snacking on scuds this whole time. I managed to catch one right away, but the other's gonna be a bit more of a challenge with the tower in the way. The surface algae had actually decreased since adding the scuds, so I'll try to catch the other Cory this weekend.