not knowing the dimensions of the the smaller tank i guessed roughly 20 inches dimater by 40 inches long. yields a capacity of just under 55 gallons. Keeping the same diameter that volume increase would change the length by roughly 17.5 inches (so 20x57.5)
Or we could go from a 20x40 to a 24x40, that yields the same volume change.
volume in Cu/In=3.14*radius^2*height The radius is half the diameter.
Divide our answer above by 231 and that yields gallons.
I put the above formula into an excel spreadsheet, that allows me to change one number at a time and get an instant result.
Sorry for the math lesson
