The brochure states that the pool is 28,017 gallons. By the formula using average depth I get about 35,000 gal (using rectangle shape in calcs) The pool is 40'6 X 20'6" GRECIAN style or very long octagon ( 8 sides) 3 ' deep on shallow and 8' deep on deep end. Are the answers different because the pool is not a rectangle? 7,000 gals seems like a lot of difference to me. I want to select the correct pump and filter size. Would 7,000 gals make a difference? Would like to turn water over every 8-10 hours. Do I need more than 2 returns? May add a water slide and fountain in a couple years and a SWG. Any input is appreciated.