Hi, lurked here to solve past issues but this one has me scratching my head. I've recently noticed that my filter doesn't appear to be working any longer. I had some algae appear a few weeks ago, so I shocked the water and brushed as I usually do but the water isn't clearing. I went to check the filter pressure, the gauge reads zero. Thinking I had a bad gauge (since flow is fine) I tried to backwash the filter, when I did the sight bubble stayed clear, usually backwash is very dirty. The multi valve appears to be working, since backwash sent water out the discharge, and 'filter' does not. Any ideas?