While the Otocinclus are known for their algae-eating trait, they also partake in a variety of vegetables, including cucumbers. Simply blanch the cucumber and secure it to the bottom of the tank. Over time, you may even find your Otos nibbling away at it.
However, cucumbers or any other vegetable should not replace algae as their primary source of nutrition. Algae forms the basis of their diet, and vegetables should be seen as supplemental foods. Feeding a balanced diet with varied nutrients ensures the health of your Oto.