When I start the filter it is around 13-14 psi, after about 30 minutes it jumps to 20. We just changed the sand in the filter, so that is not the problem. The water is blue, but cloudy. Backwashing brings pressure down, but jumps back up after about 30 minutes again. Water is definitely not moving around as much when pressure is higher. Water movement seems normal on recirculate. Gauge goes to 0 when filter is off, so gauge appears to be working fine. Pool is 24ft. round above ground. What should I do next?