Quote Originally Posted by CarlD View Post
if sized and maintained correctly
. . . and that rarely happens on AG pools, especially, with AG pool sand filters.

Undersized DE and cartridge filters still filter effectively, but just have very short (maybe, very very short) filter runs. Undersized sand filter do not filter effectively, and result in cloudy pools that won't clear up. Undersized or dirty filter cartridges, when coupled with high head (high pressure capable pumps, which include most inground pumps) can collapse, though this tends to be more of a problem on heavily used commercial pools (like the ones I've serviced) than on residential pools.