First, don't worry so much about your otoes. They do eat on plants, and decorations that others just pass by.
I use Algae wafers and my balas eat them as well as the mollys all the fish seem to like them, so it isn't a waste. Some like the mollys really need them for roughage.
IF you are really worried about your otoes, you can take a rock and sit it in a pan of water, with fish tank water for nitrates, under a light kept on 24/7 . GROW some algae, and switch this rock out put it in the tank for your little kids to graze, and have another growing.....
