Yes, you do need to feed them. What to feed them partially depends on the species. Some require wood in their diet (clown, candystripe). Some larger common plecs go for a lot of meaty food (like zebras) and should be fed accordingly. Most all plecos should be fed algae wafers and fresh zucchini, lettuce, cucumbers, etc. But they do need to be fed and not made to rely solely upon algae which is not always sufficien