Every time I see a public aquarium set up something like this they used acrylic that was at least an inch thick. The 'groove' would cause a problem if the pane flexes, making it more susceptible to breaking. The non-groove installation allows the pane to flex without having a fulcrum/lever effect across the pane.
Someday I want to know what you do to be able to afford such giant setups. I'm just a little jealous.
