I got a sample of Ken's fish 5 stick blend and there are some earthworm pellets in it. They love them as far as i can tell. Frozen Bloodworms or shrimp pellets also and high protein food. I only put a little in the tank at a time because my Giant betta will try to eat what he can and get bloated.
Ken's Fish 5 stick blend is probably the absolute best sinking food I have ever seen my fish, cories, snails, african dwarf frogs and ottos react to. I drop a few in the tanks and watch, it almost causes a riot between them all trying to get to it. Watching the ghost shrimp in the tank fight all the other critters off is hilarious. I won't however put it in a shrimp only tank, it turns very soft and I am pretty sure it will cause issues in the substrate because pieces of it float up and around the water very quickly with fish in the tank it shouldn't be an issue.