I agree 100% with 1077's post. I have 6 ottos in my tank, purchased as a group about 3 months ago. All are doing very well. They even survived a move across town. But they were placed into a well-established planted tank with lots of algae and enough dying leaves for them to munch on. I have another tank with plastic plants and no algae growth, and I doubt they would last a week in there.
I feed flakes, shrimp pellets, algae wafers and bloodworms to the other fish in that tank, and I've never seen the Oto's go near any of that food. It's algae all the way for them.
I wouldn't put them in anything but a well-established and well-planted aquarium.