Well I'd skip putting metal objects in my fishes food and I'd leave it over night. How long did you leave it? I drop a chunk of Zucchini in at night and in the AM it's all gone except the outer ring. I have seen the Plecos sucking the life out of it when I walk by at night. Keep trying, they will take something.
if he gets hungry enough, maybe he'll think the new foods are a little more appetizing. Try not feeding him wafers for a couple of days and see how he goes.
Jazzy has it right. No algae tabs for a couple of days, vege instead. Once your fish gets hungry it will experiment with other things in the tank and get a taste for vege ala fork.
Once they realise those strange chunks of stuff are edible they will prefer it.