The most common type of filtration system in a swimming pool in South Africa is a sand filter. In the “old days” before sand filter was so popular, the diatomaceous earth filter (DE filter) was the standard type fitted to swimming pools.
These were extremely effective as it could clean the pool water to smaller micron than filter sand. The result of such clean water was less sanitiser chemicals were needed to maintain a healthy chlorine residual.
The reason the sand filter became so popular was because cleaning or servicing the DE filter was laborious. The sand filter only requires a quick backwash and rinse and it is good to go again.
The media used in a sand filter is silica sand. It comes in different grades or sizes, and has jagged edges to catch the dirt particles in the pool water. The best way to gauge when the sand filter needs to be backwashed is to have a working pressure gauge fitted.
When to backwash
The “clean” pressure – that is when the first new lot of sand is added into the filter tank – should be recorded (with a permanent marker) on the filter tank. Once the pressure reaches 50kPa over the “clean” pressure, the filter should be backwashed and rinsed.
If no pressure gauge is fitted to the filter, backwashing once a week in summer and once every two weeks in winter should be fine. Remember, the more swimmers in the pool and suntan lotion that goes into the sand, the quicker the pressure will build up, leading to more frequent backwashes.
The average filter has 10 000 litres of pool water an hour pumped through it. If the pump runs for 10 hours a day, that is
100 000 litres a day. After a week of backwashing – that’s 700 000 litres of water – it’s impossible for a two or three minute backwash to remove all the dirt from the sand that has been filtered over a week. Only the surface dirt is removed.
This is why it becomes necessary to recondition your filter sand by using filter sand cleaner twice a year. For best results, use one treatment before the swimming season starts and one after the swimming season ends.
Depending on how much the pool is used, the sand will need to be changed completely every two to five years.
BLUPOOL can service your sand filter as and when necessary, click here to contact us.