Try a mussel. Black shelled guys they sell live in bags. Most places will give you a few if you ask. Cut it open, rubberband it to some rock of something so it doesn’t flip over. I feed one every other day to mine, he’s been good for years and just picks on the rocks for other food. He’s never shown any interest in anything else. If he goes for it, buy a bunch and freeze them right away. Mine still eats frozen.