When I do tank maintenance, I always clean the back glass very lightly, especially for the Otos. My four originals barely move from there to eat. The new ones I bought a couple of weeks ago, though, are all over the plants at the front of the tank and have definitely got fatter since I bought them. I also have ten Corys and about ten minutes after lights out, I drop three halves of Tetra Tabimin at each end of the tank and in the middle. The Otos wait until the corys have broken them up further before diving in for their share. Otos are not stupid!.