Backwashing

• Sand filters are cleaned through a process called backwashing. In normal operating mode, water flows into the top of the filter, then downward so that it encounters the sand grains. When the filter is being backwashed, water from the swimming pool flows in through the bottom of the filter. This clean water clears out the debris that has been collected by the sand grains, and sends it out of a waste exit on the filter.
  
  

Backwashing Concerns

• The major concern with backwashing a sand filter is that this water is coming from the swimming pool and exiting the filter as waste. Depending on the size of the pool, backwashing the filter normally uses up a few hundred gallons of water. This means that the pool water level drops and needs to be replenished after backwashing. This newly added water needs to be tested to determine if it needs additional chemicals to be safe for swimmers.
  
  

When to Clean

• When the pool is being used often, as in swimming season, the sand filter needs to be cleaned at least once a week so that it continues working properly. Also, to adequately monitor the filter and perform cleaning duties when they should be done, perform regular checks on the filter's pressure gauge. When the pressure shown on the gauge climbs to 8 to 10 lbs. above the clean pressure range, clean the filter.
  
  

Changing the Sand

• After a period of time, if backwashing fails to adequately remove the debris from the filter and properly clean the sand, the sand needs to be replaced. Continuing to backwash the filter will not be enough. Empty the filter of sand and add fresh sand.