Parboiled zuchini is a good food for them. Also, the algae wafers will work well. You can also offer worms such as frozen blood worms. I don't know any reason you couldn't offer cucumbers. I don't know about spinach...it has a very high oxyalic acid content. How much to feed? That's hard to answer for a bottom feeder. I would think if you put food in at night and some is still there the next morning, I would cut back a little. My pleco pretty much devours anything I put in there for him, but he's pretty large. Something to watch for on these fish is a shrunken stomach. Another thing is their eyes. If their eyes appear to have sunk back in their heads, they aren't getting enough to eat. They will also eat flakes that sink to the bottom.