I like figuring out Magic tricks, this one had me stumped for about 1 1/2hrs.
I finally figured it out.
Hint: Watch the guy in the baseball cap behind the 2 girls. That's how the card gets In the tank. If you want to know how he gets it out...That's even easier. :shhh:
Don't read any further if you don't want to know...
There are 2 pieces of glass on the front and 2 on the back. Look at the canopy...That is hiding the second piece of glass. These can be slid up and down. If you watch the guy in the cap, he takes the card that the girls marked and puts it on the inside of the tank (second sheet of glass). The back side where he reaches into it is 2 sheets with notches. That is why water leaks out while he is moving, but not while his arm is stationary in the tank.
This tank is obviously not part of the exhibit. They are surrounded by saltwater, and yet in the middle of this room is a freshwater tank...made for the trick.