I am researching AG Pool filters and would like to know how the measurement of Square Feet in the filter relates? I have a 21' X 43" x 54" oval AG Pool, around 30K gallons. The Cartridge system we have in the 9 year old pool is leaking terribly and getting worse so time to replace. The present filter I believe is a 100 square foot but I am not sure, and I clean it every other week or so. I see filters from 50 to 325+ square feet and would like to know how they differ and what is best for my pool. I replaced my pump last year so only need the filter. My pump is a 2HP 2Speed Waterway Millennium Hi-Flo.