The standard backwash rate for most sand filters (especially in swimming pools) is 15 to 20 gallons per minute (gpm) per square foot of filter surface area, or roughly 37 to 50 cubic meters per hour per square meter of filter area.
Filtration and backwash rates are calculated by dividing the flow rate through the filter by the surface area of the filter bed. Typically these rates are measured in gallons per minute per square foot of filter bed area.
The net effect is that too much, or too frequent, backwashing actually reduces the sand filter's efficiency. Finally, make sure you always turn off the pump before you either move or reset the filter valve setting. If you don't, you're going to damage, and maybe destroy, the system.
If you don't backwash your sand filter for some time, you may notice your water getting cloudy or more debris making its way to the surface of your pool water. Other maintenance tasks are still essential, but none will replace the need for backwashing the pool's sand filter..
All pools lose some water daily due to evaporation. Under normal conditions, expect about 1/4 inch per day, with weekly losses typically ranging up to 2 inches at most. However, factors like high temperatures, low humidity, wind, and pool activity can increase evaporation, leading to greater water loss.
Step-by-Step Guide to Crystal Clear Pool Water
If backwash rates are too high, significantly more media could be lost— compromising filter performance. In any case, it is important to measure, track, and replace any missing media during your annual filter inspection and maintenance check.
Sand Filters
Sand filter media are what filter debris out of the pool and can be made of glass balls or silica sand media. Sand filter media have a lifespan of seven to ten years before needing to be replaced.
General guidelines suggest that for every 50,000 litres of pool water, a sand filter with a flow rate of around 200-250 litres per minute (LPM) is ideal. This ensures that the entire pool volume is filtered efficiently every 4-6 hours, a common turnover rate for residential pools.
What is the Filter Backwash Recycling Rule? The FBRR requires filtered surface water suppliers using conventional or direct filtration to, where needed, change the return of recycle flows in their plant's treatment process.
If you fail to rinse after backwashing, the overall quality of your pool water can decline. Backwashing a filter aims to remove contaminants, but if you fail to rinse the filter after backwashing, you are at risk of putting those same contaminants into your swimming pool.
Pool shock is a chemical treatment that helps break down contaminants – such as leaves, dirt and debris, even oils from your skin -- that can gradually build up in your pool water. Shocking your pool as part of your weekly pool maintenance routine will help keep your water clear and balanced.
Run the backwash until the water in the sight glass (or the water you can see exiting) runs clear. Rinse Cycle: After backwashing, switch the filter to the rinse setting. Run it for 1-2 minutes to clear out any remaining debris and prevent dirt from re-entering the pool.
In general, you should backwash your filter if the filter gauge pressure reads above 10 PSI or you notice a weak flow of water out of your return jets. But you'll need to backwash more often if you have an algae-infested pool or you've just used a pool flocculant.
As a general rule, you should be backwashing your pool about once a week or in conjugation with your scheduled maintenance. Another industry standard is to backwash when your filter's pressure gauge reads 8-10 PSI (pounds per square inch) over the starting level or “clean” pressure.
One possibility is that the filter grids or Flex tubes are clogged with minerals or oils. You should clean your grids once a year, or season, with a degreaser and if needed an acid bath.
Use Pool Clarifiers
Pool clarifiers effectively address mildly cloudy water. They work by binding tiny particles together, making them large enough to be filtered out. Add the pool clarifier after the water has circulated and the chlorine shock has dissipated.
Baking soda, also known as sodium bicarbonate is naturally alkaline, with a pH of 8. When you add baking soda to your pool water, you will raise both the pH and the alkalinity, improving stability and clarity. Many commercial pool products for raising alkalinity utilize baking soda as their main active ingredient.
Stabilizing Pool Chemistry
Sometimes the pool's alkalinity fluctuates because of heavy rainfall, frequent swimmers, or too much chlorine being added during shock treatments. In these situations, adding a calculated amount of baking soda for pools helps restore pH and alkalinity balance.
How Much Should a Pool Evaporate in 24 Hours? On average, swimming pools lose about a quarter of an inch of water each day, yet variations in wind intensity, humidity, and sunlight can drastically change water loss rates. Some of the strongest and most intense wind in the country can be found in mountainous regions.
Frequently Asked Questions
Add chlorine regularly (daily or every few days) to keep a steady level, and shock about once a week if needed. What chlorine, pH and alkalinity levels should I aim for? Target chlorine 1–3 ppm, pH 7.2–7.6, and alkalinity 80–120 ppm.