For those that are interested in how to figure psi of a fluid column I added an explanation we use here at work.

1 cubic foot contains 7.48 U.S. gallons.

A fluid weighing 1 ppg would weigh 7.48 pounds per cubic foot.

The pressure exerted by one foot height of fluid over the area of the base would be:

7.48 (lb\f) \ 144 }(in^2)} = 0.0519 psi (rounded to 0.052).

Therefore, a one foot high column of 1 ppg fluid would exert 0.052 psi on its base.

Fresh water weighs 8.3454 pound per gallon.

0.052 is the pressure gradient, psi/ft, of 1 lbf/gallon fluid.

So with my diffusers at 8' then the hydrastatic pressure on my 9" disc is 8' x .052 x 8.3454 ppg (fresh water) = 3.47 psi.

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