If you think your tank is too big or someone tells you not to get that big tank….I present to you..the AQUADOM!
from wiki….
The AquaDom in Berlin, Germany, is a 25 meter tall cylindrical acrylic glass aquarium with built-in transparent elevator. It is located at the Radisson SAS Hotel in Berlin-Mitte. The DomAquarée complex also contains a hotel, offices, a restaurant, and the aquarium Sea Life Center.
The AquaDom was opened in December 2003. It cost about 12.8 million euros. The acrylic glass cylinder was constructed by the U.S. company [1]Reynolds Polymer Technology. The outside cylinder was manufactured on-site from four pieces; the inside cylinder for the elevator was delivered in one piece. The Aquadom is the largest acrylic glass cylinder in the world, with a diameter of over 11 meters, built on a 9 meters tall concrete foundation. Filled with about 900,000 liters of seawater, it contains some 2600 fish of 56 species. The feeding of the fish and the cleaning of the fish tank is performed daily by divers.