How do pool sand filters work?

For most pool owners, knowing how their pool sand filter isn’t really as important as knowing that it’s working, so since you’re here, that just means that you’re really invested in making the best of your pool, so good job! Now before we go into the inner workings of pool sand filters, here’s Tom with a quick overview of our Water TechniX Sand Filters to make it easier for you to follow what we’re talking about in this blog.

How pool sand filters work

First of all, the water goes into the pool’s skimmers, into the pump, then in through the multiport valve and then depending on what the valve switch is set at, water is routed to wherever it needs to go. Think of your multiport valve as your crossing guard, the setting dictates where the water goes.

WARNING: Always turn off the pump (unplug it to be safe) when switching the multiport from one setting to another. Switching settings while the pump is running at the very least can damage your system and can cause serious accidents.

The “Filter” setting

This setting will be where your pool sand filter will be at 99.99% of the time. This setting will spray the water from the multiport all over the sand inside of the filter. Think of a sprinkler, spraying the water all over the surface of the sand inside of the filter.

The water then flows through the sand, gently being exfoliated, trapping tiny pieces of debris as the water flows down through the sand, leaving only crystal clear water when it reaches the bottom of the pool sand filter. Once it reaches the bottom of the filter, the water is then collected by the “fingers” inside of your pool sand filter (they’re called laterals, by the way) and then expelled back into your pool via the returns.

As it is filtering the water, dirt gets trapped first on the top layer of sand, caking as it goes along making it tighter and harder for the water to reach the bottom of the sand filter. When this happens, the pressure reading of your pool sand filter will rise, and this will be a good indication that it is time to backwash your pool sand filter.

The “Backwash” setting

The backwash setting reverses the flow of water through your pool sand filter and pushes water through your filter from the bottom or from the laterals. What this does is it breaks up the caking of your sand and essentially stirs it and dislodges all of the trapped debris. The water is then expelled through the side/back port and out to waste.

We recommend getting a hose and expelling the water to a pesky neighbor’s yard, no, just kidding, really, we’re kidding. Lead the hose to a storm drain or dispose of the water according to your local regulations. This is basically how you clean your pool sand filter. For more information on how to backwash your filter, check out our backwashing guide by clicking on the button below.

The "Rinse" setting

This setting is basically just used after backwashing or after replacing your sand pool filter media. What this does is water comes out from the top, much like the filter setting, but the water is still expelled through the side/back port. This allows the sand to be pushed down and be compacted so that it will filter your water properly. Skipping this step will leave you with loose sand and it may lead your filter to spit out sand back into your pool for a good minute.

The "Waste" setting

This setting basically tells your multiport to bypass the filter completely and expel water directly out the side/back port. This setting is only used if you want to drain your pool of excess water or if the situation calls for it.

The "Circulate" or "Recirculate" setting

This setting will also bypass the filter completely, but instead of dumping the water to waste, it circulates it back in to the pool. Some situations will call for this, especially when you’re applying a lot of powdered/solid chemicals to your pool that will need to properly circulate to dissolve. To know when to set your pool sand filter to circulate, be sure to check out our blog posts dealing with pool chemicals through the button below.

The "Closed" Setting

Nothing in, nothing out. This is basically the “off” setting for your pool sand filter. NEVER run the pump with the multiport set on closed. This setting is only used when you’re servicing the pump or the filter. Again, NEVER run the pump with the multiport set on closed.  

Pool Sand Filter Media Replacement

Every three to five years, you’ll need to replace the sand in your filters to keep water filtering levels optimal. Read more about how to change your pool filter sand through the button below.


Pool sand filters, in our opinion, are the best pool filtration systems out there. They’re super easy to maintain and clean (backwashing only takes a few minutes) and you don’t have to keep changing out the filter media. Not only that, they’re extremely durable and they can take whatever you throw at them, unlike cartridge filters that can give up under certain conditions.

If you’re just thinking of building a pool, replacing an old filter, or thinking about switching from cartridge filters to sand pool filters, we highly recommend the Water TechniX Sand Filter Aspire. It’s the best selling sand filter on our site and it’s backed by Mr Pool Man’s bulletproof warranty which means that you’ll never have to worry about service and parts availability ever again.

Do you have any questions about this topic or the featured products? No worries, we're here to help! Drop us a question down below and we'll get back to you ASAP.

Happy swimming :)

We Need This
We Need This
We Need This
Please validate your form with reCAPTCHA.
Thank you!

Leave a comment

All comments are moderated before being published