Of all the parts of your swimming pool, the filter is the most important - after all, it keeps the water clean! There are three main filter systems in common use and it’s important to understand the differences between them and their benefits and disadvantages.
Sand
Sand is possibly the most common type of filter. As its name suggests, water is pushed through a fine sand which removes the dirt and impurities. Over time, as the sand collects the dirt it becomes less efficient and the water flow drops. To clean the filter you ‘backwash’ it simply by running it in reverse to get rid of the dirt and dirty water. You then switch to rinse mode which repacks the sand. You need to do this every few weeks.
The sand itself will eventually wear, just as moving water wears down pebbles, becoming more round and less effective at trapping dirt. It’s usually recommended that you change the sand every five years although some pools have run for much longer without a change. But as the sand become less effective, the system has to cycle more often, it will require more backwashing and more sanitizer.
You can use normal pool filter sand but you can get special sand such as zeolite which is hexagonal in shape and filters more impurities than normal filter sand. It costs more but your water will be cleaner.
You can also add a little Diatomaceous Earth (coming up) to increase the filter’s ability to remove small particles.
Cartridge
Cartridges use a filter material with a larger surface area than sand, typically 100-300sq ft, so they don’t fill as quickly. They are designed to run at a lower pressure than sand filters so put less strain on the pump.
Cartridge filters come in a range of prices but the cheaper ones will not last as long as the more expensive one which may last for five years or longer. Filters need to be cleaned but, depending on use, a good cartridge filter might last a season. Even with heavy use it might only need cleaning twice a year.
Cartridge filters are usually finer than filter sand but you may also be able to add a little Diatomaceous Earth to it, too.
DE (Diatomaceous Earth)
Diatomaceous Earth (Also technically knows as diatomite or kieselgur) is the fossilized remains of diatoms, a hard-shelled algae. It’s occurs naturally as a soft siliceous sedimentary rock which crumbles easily into a near-white powder.
Being so small it can filter out very small particles and keeps the water very clean. However, as it is pushing the water through smaller ‘holes’ a DE system requires more power than sand and cartridge filters.
Like sand filters, DE filter require backwashing and can be refreshed by adding more DE powder.
The Best Filter System
Pool Attendants and owners may well have their own favourite filter systems and be prepared to argue the point. Which one you choose is up to you - and your maintenance man! Sand is robust and a solid choice. Cartridges are low maintenance while DE will give you the cleanest water. However, as we’ve already said, you can add a little DE to sand or cartridge to improve the filtering.
As far as maintenance goes, cartridges probably have the edge so if you want a system you can set and forget (for a good while!), it’s a good choice.
Just remember that all filter system need care and regular maintenance will not only improve the quality of the water but reduce running costs.