I agree with all of the above here, I have 5 otos in a 29G and they are very shy. At times I have to really look closely to find all 5 of them, and mine are fat, really really fat.
They eat any algae that appears in my tank before I even get a chance to clean it, but they have not touched the hard algae that grows on the tank walls, I have to manually scrub at this.
Even though they are shy, they are also amusing, I moved a plant from my 55G to my 29G earlier today, the plant had a good amount of brown algae on there, I went down again to check the tank a few minutes ago, and it looked like I was growing an oto tree (I wish I had my camera handy), all 5 of them on the one plant, I can guarantee by morning that plant will be spotless.