Hello Steve,
Yes, you are quite right. I have seen otos and cories in very clean, bare tanks elsewhere. How they sell them I will never know. On the algae wafer problem, I asked the LFS what they fed the otos on, in addition to the algae in the tank. He said he uses Tetra Pleco Multi Wafers, which I bought (inevitably!). He told me to add one at "lights out", so that the other fish don't get there first, which I have been doing occasionally. It is a "2 in 1" wafer, with an algae disc in the centre. They loved the algae disc, but left the rest, which was removed. Now, I break it up and just give them the middle bit. The plan is to have an algae "standby" for when they have cleaned the tank. They are doing a first class job, and are incredibly active at night, but still have some way to go. Thanks for all the wonderful advice, this site is a first class education in fish keeping.
Skittler