I was doing some reading, and basically the overall consensus (from the few sources I read) are that Hikari frozen mysis is the preferred food for seahorses. It is small enough and nutritious. And your other corals will eat whatever lands on them. You may have to feed the horses with the pumps off briefly so they can get enough food. Feeding them twice a day is a good idea, because they don't digest the food as much as we'd like. What they poop out is partially (or mostly) undigested, so frequent feedings are best.
I feed Casper twice a day if I can, but she's done fine when I feed only once a day.