How do you know when to change the sand?

There's usually no need to change the sand in a sand filter. There are a few instances where the sand needs to be replaced but they are not a result from the sand wearing out or just getting old. The sand is already millions of years old when you buy it.

Converting a pool that had been using Baquacil to Chlorine needs the sand replaced after the conversion. Sand that is heavily calcified might need to be replaced because it clumps together and creates channels that allow dirt to pass through. The majority of problems that people attribute to the filter are actually problems with the water.
 
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