Could you clean the aquarium's surface with a product like Bon-Ami and then apply Rain-X or DuPont's similar product?
From the MSDS on Rain X The Invisible Windshield Wiper...
Its active ingredients are Silicone Oils, Siloxanes and Silicones, di-Me, hydroxy-terminated. These chemicals form Si-O-Si bonds with the surface of the windshield and have Methyl-terminated hydrophobic tail group which repels water. So, it should only work on true glass that is silica based, as the bond will only form with the Si-OH groups that are on the surface of the glass.
G-Si-O-Si-O-CH2-CH2-CH3
L-Si-O-Si-O-CH2-CH2-CH3 ---> Water
A-Si-O-Si-O-CH2-CH2-CH3 ---> Water
S-Si-O-Si-O-CH2-CH2-CH3 ---> Water
S-Si-O-Si-O-CH2-CH2-CH3