We suspect our filtration system on our new pool may not be achieving the required 8 hr turnover. Is there a cost-effective way of confirming the rate? Long story, but the system barely pushing enough water through a sheer descent even with ALL returns closed. It was checked for a blockage. Nothing was found. The back pressure doubles (15 to 30psi) whenever we operate the descent. If we have to, we'll live with this performance, but it just doesn't make sense to me. Any thoughts?