There aren't any confined places I know of in the Tampa area that would do other than pools.
For the open water, The Gulf vis is usually not so good in the 21 foot deep range. On the other hand, if it'll only be 1 on 1 and you have a boat, you could just run West until you hit 22 feet of water.
Short of the Gulf your better off in a spring as vis is perfect. closest one to Tampa would be Weeki Wachee. Big spring, and family could watch from the underwater observing theater. Rainbow river is next closest. If you don't mind a slightly tanic/coffee tint to the water you could always do the OW at the Hudson Grotto. They have a platform at 20 feet, 40 feet and 100 feet. The dive shop across the street does their OW there, and it's much closer than the 2 previously mentioned places.
Hope that helps.