BioLab Info

THE SAND FILTER

How It Works

Common High Rate Sand filters use a specific grade of sand (#20 Silica) to do the filtering. The sand fills approximately half the filter tank, providing adequate freeboard (the area above the sand) to allow proper backwashing.

Water enters through a diffuser assembly pipe at the top of the filter. Once inside, it disperses onto the top of the sand. As water seeps through the sand, the debris is captured on the microscopic, jagged edges of the sand grains. The now filtered water is collected at the bottom of the filter tank through a lateral assembly. The lateral assembly is designed with slot openings just smaller than the diameter of the #20 Silica sand. Water's allowed to pass through them, but not the sand.

Advantages

Sand filters are popular for several reasons:

Easy to maintain
Low cost
Removes particles as small as 25 to 40 microns. (Although other filters capture smaller particles, many pool owners find this level of filtration acceptable)
The use of a water clarifier, like Polysheen Blue™, on a regular maintenance basis will provide excellent water clarity for any pool using a sand filter.

Backwashing the Filter

When the filter pressure reaches 8 to 10 psi (pounds per square inch) above normal operating pressure, the water is having trouble moving through the filter and it's time to clean it. (Note from Pool Emporium, Inc.: Our experience in Florida has shown that most pools do not reach a pressure increase of 8-10 psi, but are in need of backwashing. We suggest backwashing at an increase of 3-5 psi or every two months, whichever comes first.) Backwashing rinses the loose debris from a sand filter. By reversing the flow of the water through the filter, the water stirs up the sand, knocking the dirt off the top of the sand into the freeboard area and out of the filter through the waste, or "backwash line." Hundreds of gallons of water are sometimes used to backwash a filter properly. For this reason, some municipalities in areas of limited water availability ban the use of sand filters.

The water level in the pool should be monitored during the backwash cycle to prevent the possibility of the water dropping below the surface skimmer. Should the water drop below the surface skimmer it is possible for the pump to lose prime (stop pumping) and cause damage to the pump housing.

Replacing the Sand

Many manufacturers refer to sand as a permanent medium, but it really isn't. The sand needs to be replaced every five to seven years in pools that use chlorine or bromine as the primary sanitizer. (NOTE FROM POOL EMPORIUM, INC.: In Florida we run our pools year 'round. Our pools see approximately 4 times the usage of pools in other parts of the country. We suggest you change your sand every 3-5 years.) For biguanide systems, like SoftSwim, you may have to change the sand more often; sometimes every year or every other year. The reason for replacing the sand so often in a SoftSwim pool is really a testimony to the clarifying action that is characteristic to biguanide chemistry. The biguanide molecule is a large polymer chain. As such, it attracts bacteria as well as millions of other microscopic particles. By being such an effective clarifying agent, this already large polymeric chain gets even larger with the attached particles. The filter is merely doing its job when it filters this now massive particle from the water. The pool owner must chemically clean the filter of a SoftSwim pool with SoftSwim Filter Cleaner™ every four to six weeks in order to effectively remove these accumulated particles from the filter.

Chemically Cleaning the Filter

For a SoftSwim pool, clean the filter every four to six weeks with SoftSwim® Filter Cleaner™.

Following label directions, allow Filter Cleaner to soak the sand to dissolve the build up of particles accumulated on the filter. Failure to chemically clean the filter at least every six weeks will likely result in serious water quality problems, like cloudy water or the development of pink slime or water mold in the plumbing.

In a chlorine or bromine pool remove oils with Strip Kwik™ first, and then use Kleen It™ to dissolve calcium scale deposits. Typically this cleaning should be done at least twice a season: Once in mid-season and then again before the pool is closed for the year. If the pool is maintained in operation throughout the year, an additional cleaning should be done in the spring.

Notes on Changing Sand:

Use the right sand... #20 Silica Sand. Do not use play sand or builders sand!
When adding sand to the filter, partially fill the filter tank with water prior to adding the sand. This prevents the sand from breaking the lateral assembly.
Use the right amount of sand. Adding too much or not enough sand will be detrimental to the operation of the filter and the clarity of the water.