8.5 pounds per gallon of water x 240 gallons = 2040lbs
multiply the length by the width in inches (assuming 10'x2'=120"x24") = 2880 square inches.
2040/2880= .71 pounds per square inch.
I guessed on the dimensions, and the weight will be higher becuase of the acrylic, stand, filters, rock, etc. 1.2psi is not an unlikely number for the final.