Sometimes, a stable and well-cycled tank may not be able to produce enough soft algae to sustain an otocinclus. It’s highly recommended to supplement your otocinclus’ diet with algae wafers, fresh vegetables, blood worms, or sinking fish pellets every few days.
That said, there’s no need to feed your otocinclus every day since it prefers munching on algae compared to any other food. Try feeding it two times a week. If it still seems hungry, increase its feeding frequency to three or four times a week.