Sand filters are low maintenance filter systems. You can let them run a long time without any maintenance – the dirtier they get, the better they work. Sand filters should be backwashed only when indicated by the pressure gauge or water flow back to the pool. You should chemically clean the sand once or twice a year. The sand itself can be replaced annually for easier winter storage, but sand can last up to 7 years.
Sand is the oldest and most common method of pool water filtration. All sand filters have a few things in common:
- Sand filters are filled with a special sand, known as pool grade #20 silica sand. This type of sand has sharp edges, which separate and capture small particles, effectively filtering the water.
- When in the filtration mode, water flows through the sand, from the top of the tank to bottom.
- Sand filters operate on the basis of "depth" filtration where dirt is driven through the sand bed and trapped in the spaces between the sand particles. Initially, a clean sand bed removes larger particles, and then, as the bed starts to load up with dirt, the filter removes finer particles.
- An underdrain at the bottom of the tank holds in the sand while allowing clean, filtered water to pass through.
- When the sand finally becomes saturated with dirt, the pressure inside the tank will rise and the water flow will begin to slow.
- The sand can be cleaned by "backwashing" which involves reversing water flow through the filter, sending dirty water out the "waste" line.
Tips for sand replacement:
- When replacing the sand make sure you first run water into the tank enough to cover the underdrain/laterals at the bottom of the tank. The water will cushion the blow of the incoming sand.
- Make sure you cover the center pipe so sand does not get inside of the center pipe. The center pipe is where the clean water goes back to the pool – any sand in the pipe will end up in the pool.
- Once you have finished replacing the sand, wet down the fresh sand before closing the tank. This prevents dry sand dust in the tank from shooting into the pool.