Why is Sand in My Pool?
First, are you sure it’s not just sediment? Sediment in the bottom of the pool often looks like sand; however, sediment, when brushed, tends to disappear. Sand, when brushed, tends to immediately resettle. Sand that has escaped from the sand filter will normally settle in piles directly beneath the return inlets. So, be sure its real sand before opening your filter, and then see below.
Sand in the pool suggests a crack in the filter’s underdrain system. Often, a filter with a cracked underdrain will spit sand into the pool for a few moments when you return the filter to “filter” position after backwashing. Small cracks tend to seal themselves until the filter is backwashed again.
Cracked underdrains must be inspected. The filter must be opened from the top (which often requires removal of the filter valve) and the sand fully removed. Then, the filter’s underdrain system that includes the lower piping and laterals can be carefully inspected for cracks or separations. Any crack large enough to allow sand granules through must be repaired or replaced.
This procedure is difficult and most pool owners will opt to have a professional technician perform this work. It is also a good practice to change the sand at the same time the underdrain system is inspected and repaired.