Pressure gauges fail quite often. A good barometer for you to get accustomed to is to simply look at or feel the water pressure returning into the vessel out the jets. When the water flow slows dramatically, the filter(s) should be cleaned or backwashed (sand filters only). Most people owning sand filters backwash them way too often. If you want the filter to grab finer particles out of the water you need to let the pressure build and the water flow to be reduced. Sand filters work much more effectively when they become dirty and partially clogged. The dirt and gunk that was filtered actually helps to filter more of the same. So, if the water is pushing with great force into the pool, hot tub or swim spa, the filter is fairly clean. You want the water flow to slow down over time. This means that the filter is working. However, there does come a point in time when you MUST-backwash or clean the filter.
