We are getting ready to build a pool with 380 sq. foot surface area, a max depth of 5 feet and a 7"x7" raised spa. Our builder quoted a Pentair clean and clear plus 420 filter. I asked if it would be smart to upgrade to the 520 filter. They told me that the 520 would only give me about a week longer run time between filter cleanings over the 420. Does this sound right?