I agree with steve. After lights out is the best time to put in his food. Along with the algae waffers. He/she would love some veggies. Squash, cucumber, zucchini, spinach, green beans, they even like melon too.
My Pleco loves zucchini. He gets a fresh slice every morning. He's usually in the same spot every morning too, waiting for it. I have the same issues that sinking wafers and pellets rarely make it to the bottom of my tank.
I just slice it round and weight it down. I use the old pewter plant weights and let it sink to the bottom. If you feed them at night, remove any zucchini that wasn't eaten the next morning.
I've moved your thread to the Cat Fish/Pleco section of the forum.
You could also grow some mossy rocks. Put some nice flat rocks in a glass jar or container of water and set it in a sunny spot. Rinse and change the water every couple of days. You should eventually have moss growing on the rocks. The other fish may ignore the moss, but the pleco will enjoy it. Mine do.