How big is it? Juveniles should be fed more often - really small ones can be fed once a day. After that, a few times a week should be fine. Just be sure the tope is secure - they can get through any opening small enough to squeeze their surprisingly small heads through.
Also, don't rely on krill. It's ok to get him eating, but should not be a staple. You should give him a variety of meaty fare - squid, scallops, shrimp, etc. Buy frozen seafood mix (as long as their raw and unseasoned) and cut it up into pieces about the size of a pencil eraser until you know what he can handle.