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How Do Pool Sand Filters Work? A Thorough Overview

Sand filters are typically the most budget-friendly and commercially-used pool filters available. People often wonder how sand filters work since they don’t have cartridges or fins to support the filtration process.

Pool sand filters work by compressing sand with water. The pump pushes the pool water through the sand, filtering anything down to 20 microns. You can clean a sand filter by backwashing it, which flushes the dirty debris out of the tank. Every pool sand filter uses 20-grade silica or Zeolite sand.

In this article, I’ll explain how pool sand filters work, how often you need to change the sand, and how your pool’s chlorine works with the sand filter.

I’ll also show you why sand is a popular choice among above-ground pool owners and commercial properties. Let’s get started!

How Do I Know if My Sand Filter is Working?

You know if your sand filter is working if the water looks clear, the sand is compact, and the filter has a PSI between 10 to 25.

The filter’s PSI shows there’s water pressure going through the sand and hitting the pressure gauge rather than going around it. Functional sand filters should remove most debris and oil from the water.

Here’s a list of signs that your sand filter is working:

  • Your filter shouldn’t let fine debris through the plumbing system. Sand filters typically filter down to 20 microns. You shouldn’t be able to find leaves, sticks, hair, or oil coming through the other end. Check your pool’s outlets to ensure nothing large comes through the jets.
  • Your pool pump should sound like smooth, flowing water. If your pump is making a grinding noise, the filter might have pushed some of the sand into the impeller. Functional sand filters improve the pump’s performance by removing the debris and encouraging a steady flow of water.
  • The sand filter’s pressure gauge shouldn’t be below 10 PSI. There’s likely not enough sand in the filter if it’s too low. However, older pressure gauges can fail. Consider replacing the pressure gauge with a part number provided by the filter’s manufacturer before assuming something’s wrong with the filter.
  • There shouldn’t be any sand coming out of the filter. Functional sand filters retain all of the sand after the initial cycle. Some sand might go into the pool after you add the sand, but it shouldn’t come through after that. Sand in the pool is often a sign of plumbing leaks, broken manifolds, or incorrect installations.

It’s time to replace the sand once the filter doesn’t work as well as it used to. If you’re unsure how often you need to change the sand in the pool filter, read on.

How Often Do You Need to Change the Sand in a Pool Filter?

You need to change the sand in a conventional pool filter once every two to three years. However, you might have to change the sand annually if you have a small above-ground Intex or Bestway filter.

You’ll know it’s time to change the sand when a backwashing cycle doesn’t reduce the PSI below 20. The sand will look grimy, oily, and dirty.

Keep an eye out for these clear indicators that it’s time to change the sand:

  • The filter’s PSI doesn’t drop, regardless of whether or not you backwashed the sand. I suggest removing the top inch of the sand, then topping it off with the same amount of sand. This process can prevent a full sand change by wiping away most of the debris on top of the filter.
  • If the pump doesn’t circulate the pool water, the filter’s sand might be saturated. Too much debris in the filter prevents the pump from pushing anything through the plumbing. Keep an eye on the pressure gauge and turn off the pump if the water doesn’t circulate. Don’t forget to ensure the water is above the skimmer line in the pool.
  • Change the sand after three years, even if you don’t notice a change in the equipment’s performance. Pool sand shouldn’t be used for longer than three years because it starts to leak unseen oils and bacteria into the water. You might not see the effects until the whole pool is full of algae or total dissolved solids (TDS) that prevent the chemicals from working.

Fortunately, you can backwash your sand filter monthly (or whenever the PSI exceeds 20) to preserve the sand for a few years.

All you have to do is turn the filter to its backwash setting, attach a backwash hose, and let it drain for a couple of minutes. This process removes the excess debris and lets the filter keep most of the sand.

Where Do You Put Chlorine Tablets With a Sand Filter?

You put chlorine tablets in a pool floater rather than in the sand filter. Sand is the only thing that should go into a sand filter. Place the tablets in a floater and let it move around the pool while the pump circulates the water. Putting tablets in the skimmer or filter will corrode the tank and skimmer.

Chlorine tablets are just some of the many chemicals needed for swimming pools. You can also use liquid chlorine or install a salt system.

Either way, the chlorine should never go directly into your sand filter. Sand is the only thing that goes into a sand filter.

On that note, never place the chlorine tablets in the skimmer basket or pump basket.

Chlorine is quite a corrosive substance, which is why it’s always diluted by the pool water before entering the plumbing. Liquid chlorine should be dumped around the edges of the pool while the pump is circulating.

The chlorine tablets should be placed in a floater, such as the 440 Pool Chlorine Dispenser. This floater can hold enough tablets to treat up to 25,000 gallons of water. You can also adjust the dispensing holes to choose how much chlorine is used.

440 Pool Chlorine Floater Dispenser


  • Jonah Ryan

    Jonah has worked for several years in the swimming pool industry installing and repairing equipment, treating pools with chemicals, and fixing damaged liners. He also has plumbing and electrical experience with air conditioning, ceiling fans, boilers, and more. When he's not writing for Temperature Master, he's usually writing for his own websites, and

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