I have 2 ottos.
I bought them about 3 1/2 months ago when I had a TON of brown algae. They did a marvelous job on the algae, now I've been feeding them algae wafers like you. Except, I throw in 2 or 3 because, like you, I have fish that eat the wafers too. So you might consider this.
Over the next few days, increase the amount of wafers you throw in. Like, start with 2 tomorrow for instance, and after you throw them in give it a few hours, come back and if you still see pieces of wafer, then thats too much so decrease it to 1 1/2, and go from there.
This is off topic, but I have a 20 gallon I have devoted to about 25 snails, a 5 1/2 inch long kissing gourami, a 2 inch kissing gourami and a betta. I have them all trained to eat algae wafers off the bottom of the tank instead of flakes....weird huh? When I wake up in the morning, I turn on my PC and throw in about 20 algae wafers. They adapted to their environment.
Nick