My otos are fatties just like yours, lol.
Great fish, I love them. All they do is work and get along with the other fish - can't beat it!
I have 10 in a 210 gallon and they do surprisingly well keeping it clean. Obviously it is too much to keep it perfect but they are always fat. When I had diatoms they would clear a 6in x 6in patch on my rocks overnight.