You could also try boiled Brussels sprouts. My hypostomus pleco ate that gladly, as well as cucumber raw, zucchini also raw, green beans and petite pois. My cirhorrus still eat cucumber etc... Sometimes it just takes them a while to figure it out, but if you want them to eat veggies I suggest not over feeding them on cucumber as it is more moisture than anything else and very low in nutrients, or so I was told. Just mix it up, and don't forget to make sure the veggies have not been treated with chemicals....
Hope this helps a bit...
Hope this helps a bit...