I have the same problem with Candi the betta and her cories. The best thing I've found so far is to soak the cories' pellets, which are shrimp pellets, for a couple of hours or so, then squish them into the tiniest pieces possible, then put them down a very long Starbuck's straw (actually two straws stuck together) near the substrate after lights off. Of course, Candi learned too fast for her own good that the bottom of the "green straw" means food. Took about two times. Poor little Cories, much as I think they're cute, aren't bright enough to associate the bottom of the green straw with food, but I think they're getting enough food. The busted-up tiny particles sink to the bottom. Candi only goes for the larger particles.
Not sure how this would work with otos.
Want some of the algae from my tank? I can send you a few big glumps of it.
