Replacing sand in a filter

[Cornus]

In reading some of the threads I notice it mentioned that the sand should be replaced every 3 or 4 years. What's the reason for this...seems to me that sand should last almost forever?

I haven't been able to keep my pool clear this summer. The filter is as old as the pool [20 years]. It's a liner 20' x 40' and this too is 20 years old. Although I believe in leaving well enough alone, I recognize that this is beyond the normal life of the liner. Would you suggest replacing the liner before next season? Or just wait until it actually dies? And changing the sand in the filter? Or possibly getting a whole new filter since this too is 20 years old?

Thanks for any help.

[Backglass]

In reading some of the threads I notice it mentioned that the sand should be replaced every 3 or 4 years. What's the reason for this...seems to me that sand should last almost forever?

I haven't been able to keep my pool clear this summer. The filter is as old as the pool [20 years]. It's a liner 20' x 40' and this too is 20 years old. Although I believe in leaving well enough alone, I recognize that this is beyond the normal life of the liner. Would you suggest replacing the liner before next season? Or just wait until it actually dies? And changing the sand in the filter? Or possibly getting a whole new filter since this too is 20 years old?

Thanks for any help.

Sand filters work by trapping the dirt particles between the grains. Over the years, the sand actually gets "polished" by the water, rounding and smoothing the edges of the sand and reducing the filtering capacity. It also can cake up & channels can be created in the bed. After 20 years, you will see a big difference in filtering capacity with a sand change-out. For an even better filter, replace with zeolite instead of sand for DE like filtering.