The filter is the most important part of any swimming pool system. Choosing the correct one is often a confusing task with so many types and sizes available.

The purpose of the filter is to remove dead matter and debris from the pool water so that bacteria does not feed off it and enables you to swim in a clean and clear pool.

Sand Filters

Sand filters use specially graded sand as the filter media. The water enters the filters Multi Port Valve and then travels down through the bed of sand and the dirt is trapped between the course grains of sand. The clear water is removed from the bottom of the tank through the laterals and is returned to the valve and back to the pool.

Filter Sand: When standard sand is used in the tank it can filter out debris down to about 15 microns in size, which is very small considering that humans cant see 100 microns by eye.

Filter Media: A new filter media is now available that will filter down to 3 microns and remove ammonia from the water as well (Ammonia is what algae feeds on). This filter media goes by the names of Zeolite, Zelbrite, or Zeopure. It is generally twice the price of regular filter sand, and requires some maintenance once a year to remove the build up of Ammonias in the sand.

The main advantage of the sand filter is its ease of maintenance. To clean the filter takes only a few minutes and there is no mess. Usually you will get up to ten (10) years expected life from this media.

The main disadvantage of a sand filter is that it is the least efficient, but then that is why they are larger in size. Depending on how dirty and the size of the filter, backwashing could use over 500 litres of water. This may not be practical for people with a limited supply of water such as those on tank supply. This process also wastes treated water which means the pool may have to be topped up and rebalanced after backwashing.

TIP: Always look for a sand filter that has a spun Fibreglass tank. This will give you the longest service possible. Polymer tanks can and do crack.

Cartridge Filters

The main advantages of the cartridge filter include very efficient filtering compared to sand filters (down to 10 microns), and no excessive water wastage down a backwash pipe. The cartridge can be washed on your lawn and water the lawn at the same time. Sand and D.E. filters are cleaned by backwashing. This process needs a drain into which the backwashed water and dirt can be flushed into. A suitable drain may be too far away, or you may not wish to have a pipe running across your yard, or it may be that the drain does not exist yet and/or it may be too expensive or impractical to have one installed.

There is a cartridge filter for almost any pool. They range in size from a few square feet up to 450 square foot. They are relatively inexpensive to buy and provide very good water clarity. Most cartridges are made from polyester and will last for 4 to 5 years if looked after.

The cartridge filter comes into its own in regards to size relative to flow rate. The cartridge filter is very compact. A bypass valve between the pump and filter can be used to allow for vacuuming to waste and removal of excess water after heavy rain.

To clean a cartridge filter you simply use a garden hose to hose off the dirt. This will usually take an hour. This is the main disadvantage, high maintenance.

TIP: There are high pressure nozzles available to attach to your hose that give you the perfect fan jet for cleaning your cartridge. The cleaner you keep it the longer it will last and the better it will perform.

D.E. Filters

The D.E. filter uses diatomaceous earth as a filter media. The D.E. filter has plastic grids covered with a special type of fabric. The layer of filter powder covers the grids and does the filtering, down to 3 microns.

The pump size and D.E. filter size is very important as the water flow has to be within a specific range. If the water flow is too fast then the dirt will not be trapped in the DE and clog the grid material instead. If the water flow is too slow, the dirt will not penetrate the DE cake enough. The filter size should be matched so that it will only need cleaning about once a month. This allows for the disposal of the DE powder to be kept to a minimum and to save on maintenance costs.

Although the D.E. filter is one of the best filters available for a swimming pool, they are labour intensive to clean and maintain and have therefore lost favour to most pool owners.

If any of the grid material or manifolds become damaged, the DE powder will bypass the grids, and go back to the pool. The pool is often cloudy when this happens.

Every time you backwash or clean a D.E. filter, you loose the DE powder down the drain. Therefore as soon as you backwash and clean the filter, you must "Recharge" the filter with the correct amount of DE powder again. This means there is an ongoing cost.

Depending on how dirty and how large the filter is, backwashing could use as much as 500 litres of water. This may not be practical for people with a limited supply of water such as those on tank water. This process also wastes treated water which means the pool may have to be topped up and rebalanced after backwashing.

TIP: Too much or too little Diatomaceous Earth or D.E. powder, will affect the performance of the system. Always use the filter manufacturers recommended dose, not what it says on the box of powder.