How to Backwash a Sand Filter

a blog by James

Filter Basics

One of the easiest ways to keep your pool clean is to backwash the filter regularly. Today we will go over the procedure of how to backwash a sand filter, which is one of the most common filter types. At the beginning of the season, or anytime the water is very dirty and cloudy, I recommend doing a backwash once a day until the pool is clear, typically running the filter 24 hours a day until its clear. When the pool is clear and you are doing your basic maintenance, I recommend doing a backwash once a week. The once a week backwash is also a good opportunity to check your water chemistry if you maintain the pool yourself. If you forget to backwash your filter one week, you will start to notice the pressure inside the filter increase. Most sand filters have a pressure gauge near the multiport, or valve, used to adjust the filter settings. Most filters operate between 5-15 PSI. When the pressure is up around 20 PSI or higher, its time to backwash.

When and How to Backwash

You’ll typically notice the pressure coming out of the returns is very weak when the filter is ready for a backwash. If you don’t backwash the filter when the pressure is high, it can reduce the pressure and flow back into the pool, resulting in a number of problems such as lack of chlorine distribution. The lack of flow can also cause problems with salt water systems and heaters. Long story short, your pool will start to turn green if you don’t backwash. The first thing to do when you’re ready to backwash the filter is turn off the pump. Although it seems like common sense, moving the handle of the multiport while the pump is on can damage your equipment and is not recommended. The next common sense step is to make sure your backwash hose is connected and unrolled, usually out to the street. With the pump off and the backwash line prepared, move the handle to “backwash” and then turn the pump back on. The water will flush through your filter, removing the majority of the dirt and debris that has been filtered out. You’ll typically see the water come out very dirty, eventually clearing up. Most filters you’ll want to run in “backwash” for about 1-2 minutes, or until the water starts to clear. At this point, you will turn the pump off, move the handle to “rinse”, and then turn on the pump. Typically you will run in “rinse” for about 30 seconds, at which point the water coming out of the discharge hose is generally very clear. Now you will turn off the pump one last time, move the handle back to “filter”, and then turn on the pump as usual. Now the backwash is complete. You’ll notice the pressure coming out of the returns increases after the backwash, as the water can now flow more freely through the filter.

After the Backwash

If you’re adding shock or any chemicals to your pool, I recommend doing so after the backwash to make sure those chemicals aren’t wasted out of the pool via the backwash line. If your pool remains cloudy after daily backwash, you may need to replace the sand inside of the filter. I recommend changing the filter sand every 3-5 years to ensure a clean and easy to maintain pool. If anyone has any questions, I am happy to answer them in the comments. You can also send an email anytime with pool related questions and I will try my best to get back to you in a timely fashion. Thanks and I look forward to sharing more helpful information with our customers and anyone out there who finds us online!