cut the stuff very small...if you need to feed two pieces, or daily, you can. too large will be much harder on him to eat. some people like feeding theirs clam, and some people are against calling clam food when they may introduce live clams later!
i bought a bag of korean fresh seafood buffet (no preservatives) and blended it until it was very small, then we portioned and froze it. we break out small pieces whenever we want treats for the tank.