We will not tell you that you need your sand changed in your filter every 3-5 years as many companies would have you believe. We have many clients on our maintenance programs that have had the same sand for 20 + years in their filters and still have excellent clarity in their pools. Reduced clarity is the only reason sand should be changed. Sand for pool filters is angular by nature. This is the physical characteristic that helps to acquire small particles. The velocity of water going through the filter if too high can prematurely “round off” these particles basically turning them more or less into ball bearings that do not have the capability of trapping particles as effectively. This is not a sand problem. It is a hydraulics problem. In addition, poor water chemistry can also play a role in the life of the sand. Using the wrong type or quantity of chemicals can also play a factor in the life of the sand.
Salt water pools are very popular today, but not all pools should be utilizing this technology.
In my experience, any pools that have a sedimentary rock as the predominant surrounding decking surface should understand that unless you meticulously seal these types of rock with a very small molecular product on an ongoing basis then you should expect this rock to deteriorate at an accelerated rate. Even faster than the surrounding mortar! This will become the most noticeable at the points of entry and exit to the pool.