Math may not be one of your strong points. If the tank is 2′ diameter by 10 feet deep, then the volume is 1x1x3.1416×10 which equals about 31.416 cu. ft. and if I read your answer correctly, you said there are 2.31 inches in a gallon weighing 8.22 pounds. My gallon milk bottle have a lot more than 2.31 cu. in. in them.