Lost an Oto today unfortunately, not sure what was wrong with him, all the others were fine and water parameters are normal. Being an Oto it might have just been natural.
Hope was natural causes, not starvation as is often the case with otos.
Adding stones or rocks thats been sitting in a small container with old tank water on windowsill to have direct sunlight may help get some algae on these and then add the algae stones to the tank may help supplement green algae which otos like.