I have an AG 21 ft. round pool, and sometimes when I unplug the (Jacuzzi Laser Sand) filter, water shoots up several feet out of my skimmer. It doesn't happen all the time, but it does happen every third day or so. My pressure gauge never goes above the low teens, and otherwise everything seems to be working fine. The water is clear, I vacumn, backwash and rinse every week.
Any ideas what's going on and how to stop this from happening?