Just the weight of the water would be 720 pounds (8 pounds per gallon). The weight of the glass itself would probably be at least another 50, just from having had an aquarium half that size -- I know the tank empty weighed at least 25-30 pounds. So almost 800 pounds full. one gallon of water is 8 pounds, if you fill the aquarium with 90 gallons of water, 90 x 8 = 720 pounds plus the weight of gravel, filters, decor, fish, and the tank it self. could be as high as 800 pounds. It's a little more complicated, as a 90 gallon actually holds slightly less than 90 gallons (closer to 80), and much of the water will be displaced by stone and decorations. To answer your question specifically, a typical, empty 90 gallon glass aquarium weighs about 160 lbs, and about 1050 lbs filled with typical aquarium "stuff."