Here's one for you..it's not really North Orlando but it's off 408 south of the Exec. Airport. They opened right before I moved from FL to GA . I've heard good things about them.
Orlando Tropical Fish Store | Saltwater Fish | Sps Coral | Live Rock | Aquariums | Sea In The City
here's a search from local.com
Find Aquarium Stores in and around Orlando, FL on Local.com
I've been to Ernie's Seven Seas and wasn't impressed(if it's the same people)