Thanks. but I think my calculation is correct. My pool is 3 foot on the shallow end and 6 foot on the deep. for a 4.5 average. It is a lap pool mainly for my 5'2" 73 yr old wilfe to use for her exercise. BUT I whole heartedly agree with you on the size. As a engineer who worked on the Apollo command/service module I am of the bigger is better school.1st. If you mean you have a 25 x 13 pool with a 4.5 foot shallow end and a 7.5 foot deep end, here is your size: Average the depth (6 feet) and multiply that by 25 then 13 for 1950 cu feet. Convert to gallons (7.49 gal/cu ft) = 14,600 gallons.
As far as sizing, I suggest letting the other guys chime in. But my reading here suggests large system, low % and longer run = best salt cell life.