The shrimp being suggested are FW.
I do believe that
most of these FW algae eating shrimp are filter feeders, eating freefloating diatom algae? I'm not completely sure however, so I need to go research FW shrimp
Anyways, the Oto's will eat their preferred algaes where ever they find it, on the glass, plants, decorations, substrate but not in the water column...