I don't know what kind of pleco your talking about but as for eating Pleco's will graze algae off the tank and decorations mostly at night. For extra feeding you can drop an algae tablet in the tank at night after the lights go off. Your usually not going to see it eat. Leave the tablet in there and most likely it will feed during the night sometime. You can also blanch some zucchini or cucumber, weigh down the pieces or clip them to the side of the tank, and leave in there all night. It might take a couple tries for it to try new foods but don't give up. Also I don't know what most people do but I only off "other" foods a couple times a week. Plus if you don't know Pleco's need a piece of driftwood to rasp on, it aids in digestion.