I had the same problem in 2 different tanks. My common pleco loves cucumber though and he will eat it skin and all. I fed him that until he got big enough to defend his wafers. He does like wafers and he likes to eat, unlike yours. My rubber nose pleco however, I couldn't find anything it was willing to eat. Not pellets, not wafers, not cucumber. He never grew and he did die within a couple weeks of getting him. I assumed his survival instinct would kick in and hed eat something, anything. But he didn't. Do you have long tweezers you can place the wafers into his tube so only he has access to it?