Algae eaters can't survive on algae alone, they also need "meaty" food in form of microorganisms (and probably some sorts of bacteria). I wouldn't worry much about the Otos in such huge tank but Plecos should have more and sinking tablets will work well as well as Bloodworms for example.

I have tested Zuchini with some L numbers, Otos and Gibbiceps they came on to it for a short while and never returned back to it.

Some aquarists culture algae on stones (in another tank), and once it becomes green it's been fed to the Algae eaters. That is the way I feed the "always hungry" Neritina snails in my shop.

What I have observed;
Each time I take my filter out for cleaning, some dirt normally comes out of it. My Otos go crazy sucking on leaves or anything else in that area. Filters are full of various microorganism and bacteria that these guys will feed on.

Regards, Dusko.