He may be getting enough cleaning your tank. Also you could try dropping it in after lights put. If you have just the one bottom feeder just drop a piece of wafer in so it all gets eaten. I very rarely see my oto eat either but he's rather chubby, my tank is clean and the piece of wafer I feed him about every other day is gone the next morning. You may be feeding too much, too often . Their stomach is about the size of their eye.
He will eat if he needs to. There is probably enough algae in the tank. Or he may just be waiting for it to get nice and soft. Don't worry, an Oto won't starve himself.
Also, Otos are shoaling fish and need to be kept in groups of 3 or more.
yeah I know it is it was funny when ever I add some one new to the tank the has to check out the bag and then lets them make themselves at home b4 he starts chasing them around the tank tho the cories I think love it lol