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The sand filter tank is round or egg shaped. The sand contained in the filter strains the impurities from the water as the water passes through the sand. The sand filter uses a multiport valve to direct the water through the filter or out to backwash. The valves are either top or side mount. Both valves work the same way. In filter position, the water is directed over the top of the sand bed and, as the water flows down through the sand, the sharp edges of the sand catch the particles in the water. The clean water is pushed out of the filter through the bottom lateral assembly. The laterals are in the shape of a wagon wheel, with tiny holes along the top edge, to allow the clean water back to the pool and the sand and dirt to stay in the filter.
When do I need to replace my sand?
On average, sand should be replaced every 2 years. This may be longer if the pool stays clear, or shorter, if the filter runs all the time. The jagged edges of the sand wear down and become smooth as the sand ages. When this happens the sand can no longer trap debris particles and dirt can pass through the sand and back into the pool.
If the pool is chemically balanced, the system is running the proper length of time and the bather load is normal, but the water will not clear, even using a flocculant or clarifier, then the sand needs changing.
As the sand ages, it may start to clump and the water flow can form channels in the sand, allowing the debris to pass through. Channeling is often seen when the pump horsepower is too large and wants to move too much water through the filter.