A sand pool filter utilizes industrial-grade quartz silica to remove contaminants and impurities from pool water. The circulation pump draws pool water through the skimmer inlets, pumps it through the sand filter and conveys it back to the pool through the return lines. The volume of the pool in gallons determines the appropriate square footage of sand required for adequate filtration. The manufacturer's specs for filter capacity state the maximum amount of sand it can accommodate. Matching these specifications produces the best filter performance and maintains optimum water quality.
What Kind and How Often?
Beach sand or dune sand is not acceptable as a pool filter medium. No. 20 industrial-grade quartz silica, the most common and inexpensive option, is subjected to quality control to standardize granule size. This sand removes particulates in the water down to a size of 50 microns. The medium in sand filters is normally changed approximately every five to seven years, unless events such as extreme algae contamination have occurred or toxic chemicals have been introduced into pool water.
What Can Go Wrong?
While it’s technically impossible to have a pool filter that’s too large for the job (though it may be an unnecessarily expensive purchase), a filter that’s too small for the pool size delivers poor performance. An undersized sand filter contains insufficient media to filter the volume of water delivered to it by the circulation pump. Undersizing results in reduced filtration efficiency and murky water that lacks the clarity and sparkle of a properly filtered pool. Because an undersized filter can't keep up with the load of organic contaminants in a pool, the pool owner will often attempt to compensate by adding more sanitizing chemicals, increasing operating costs and maintenance time. A too-small filter may also be overstressed by the pump output and develop damaging excessive internal pressure.
What's Your Pool Volume?
Determining the correct size sand filter begins with calculating your pool’s approximate water volume in gallons. You’ll need to know the length and width of the pool as well as its depth at the shallowest and deepest points. A rectangular residential pool without a diving board that measures 12 feet by 24 feet will typically have a depth that slopes from 3 feet to 8.5 feet. The formula for calculating the pool volume in this case is 12 x 24 x ((8.5 + 3)/2) = 1,656 cubic feet of water. To convert the cubic feet to gallons, multiply 1,656 by 7.5. The approximate water volume in the pool is 12,420 gallons.
How Much Should You Buy?
A sand filter with a capacity of 3 square feet of No. 20 industrial-grade silica is recommended for pool volumes up to 15,000 gallons. Silica filter media is normally sold in 50-pound bags. Because each square foot of filter capacity requires 100 pounds of silica, a total of 300 pounds or six standard bags of sand is required for a 12-foot-by-24-foot pool.