My Seahorse doesn't seem to be eating properly

My Seahorses before I had them had only ever been feed on frozen brine shrimp. If I feed them this I will see them eat, however I am wanting to take them off brine shrimp onto Mysis being better for them, but they don't seem to be eating the Mysis shrimp, I never see them take it.

Any suggestions on how I can wean them off to the brine shrimp and on to the Mysis please.