Fish tank on the top instead? NFT
 

Assuming you don't want to accidentally drain your entire fish tank, is it possible to build a NFT system with the fish tank on the top instead of the bottom. I say this because I live in a cold climate and I want the fish inside and the grow beds outside, but the house is elevated so if the grow beds were above the tank you couldn't get to them without a ladder.

How would you plan to recirculate the water?