I almost always have sandy sediment in the corners of the deep end of my pool--some, I'm sure, comes from my filter, but a lot of it blows in because of my location. I also lose sand when I backwash, which is fairly frequently....but when we took my filter apart last year, (after 6 seasons and open year round), the sand level wasn't noticeably low. As long as the filter is doing a good job of cleaning your water, I wouldn'lt worry about it.

Janet