What Kind of Sand for a Pool Filter? The 20 Silica Answer and What to Avoid

The right sand for a pool filter is #20 grade silica sand, with grains between 0.45 and 0.55 mm. Grains this size trap particles down to 20 to 40 microns while still letting water flow through the bed at the rate your pump is sized for. Any other sand, including play sand, quikrete, or generic construction sand, either clogs the filter, passes straight through the laterals, or both.

What is the best sand to put in a pool filter?

Use #20 grade silica sand. You can find it sold as pool filter sand, silica filter sand, or simply #20 silica. The bag should clearly state pool grade and silica. Avoid any bag that only says pool sand without a grade, or that lists the contents as sand and other minerals, because that often means a blend that includes zeolite or an off-spec grain size. Common trusted brands include HTH, Palmetto, Mystic White, and U.S. Silica Silurian.

Grain size: 0.45 to 0.55 mm

This range is small enough to trap dirt, algae, and fine debris, but large enough that water still flows through the sand bed at the rate your pump is sized for. Finer grains force the pump to work harder and require constant backwashing. Coarser grains let fine particles slip through.

Angular grain shape

Good pool filter sand has rough, angular edges, not smooth round grains. The sharp edges let the grains interlock into a dense bed and catch debris in the tiny gaps between them. Round sand, which is what play sand and most construction sand is, packs loosely and lets debris slide through. This is why a bag labeled pool grade silica matters even if a cheaper bag of sand looks similar.

Chemically inert

Silica does not react with pool chemicals. It sits there and filters. Sand that contains limestone, clay, or organic fines will raise pH, cloud the water, and foul the filter bed within weeks. This is one more reason the pool grade label matters.

What sand should you not use in a pool filter?

Never substitute play sand, paver sand, quikrete, construction sand, or beach sand. They all look like sand in the bag, but they cause different problems once in the filter.

Play sand grains are too fine and too round. They pack down, clog the laterals, and can physically damage the filter. Paver sand and construction sand contain fine silt and clay that cloud the water the moment you turn the pump on, and the haze takes days of backwashing to clear. Beach sand brings salt and organic material. Quikrete is not even close to filter grade and often contains portland cement residue that reacts with pool chemistry.

If the bag does not explicitly say pool filter sand or #20 silica, put it back.

Alternatives to #20 silica sand

You do not have to use sand in a sand filter. Two other media drop straight into the same tank with no plumbing changes. Both filter finer than silica and last longer.

Glass filter media

Made from recycled glass, angular and lightweight. It filters down to about 5 microns, backwashes faster than sand, and lasts 8 to 10 years before replacement. Glass resists bacterial buildup on the grains and uses the full depth of the bed for filtration, where sand mainly traps debris in the top few inches. It costs two to three times more than silica sand up front, but lasts two to three times longer.

Zeolite (ZeoSand and similar)

A natural volcanic mineral with a microporous honeycomb structure. Zeolite catches particles as small as 2 to 5 microns and also absorbs ammonia from the water, which reduces chloramine buildup and chlorine demand. You need about half as much zeolite by weight as silica sand to fill the same filter, which offsets some of the higher per-bag cost. First install comes with a catch: zeolite creates a fine dust cloud unless you backwash for 3 to 5 minutes and rinse for 1 minute before going into normal filter mode.

How much sand does a pool filter need?

Always follow your filter's manual. The amount of sand is printed on the tank label and in the owner's manual, usually in pounds. Typical residential sand filters hold between 100 and 350 pounds of #20 silica. A Hayward S244T, for example, holds 300 pounds. If you cannot find the manual, the fill level is printed on the tank itself in most cases, or you fill until the sand is about six inches below the top of the tank for common residential sizes.

Pour slowly. A fast pour can crack the laterals sitting at the bottom of the tank. Add water to the tank first, about one quarter full, to cushion the fall. Then pour the sand in slowly, one bag at a time.

When to replace the sand in your pool filter

Plan to replace #20 silica sand every 3 to 5 years with heavy use, or every 5 to 7 years with lighter residential use. Over time the angular grains wear smooth, the bed stops interlocking, and debris slips through no matter how clean the sand looks.

Three signs say it is time, regardless of calendar age. Pressure stays high even right after a full backwash. Water looks slightly hazy even with balanced chemistry. Or backwash intervals get shorter and shorter. Any one of those usually means the bed is past its useful life.

One factor that extends sand life is keeping large debris out of the filter in the first place. Every leaf, twig, and hair that reaches the sand bed shortens its life, and a robotic pool cleaner with its own internal basket stops most of it before it gets there. The iGarden Pool Cleaner K series is a cordless robotic cleaner that pulls leaves, hair, twigs, and fine sand into a 4L onboard basket with 180 μm filtration, which keeps the main sand bed running on lighter loads and helps the sand last closer to the long end of its replacement window.

How to replace pool filter sand

Replacing filter sand is a half day job for most residential filters. The full process works like this.

Turn off the pump and close the valves on both sides of the filter. Disconnect the multiport valve from the top of the tank. Most valves are held on by a clamp band or a union. Lift the valve off and set it aside, keeping the standpipe and laterals at the bottom of the tank undisturbed.

Scoop out the old sand with a wet/dry vacuum or a plastic cup. Cover the top of the standpipe with tape or a plug so no sand falls down into the laterals. Rinse the inside of the tank with a hose once the sand is out.

Add water to the empty tank until it is about one quarter full. This cushions the new sand as you pour it in and protects the laterals from cracking. Pour the new #20 silica slowly, one bag at a time, until you reach the fill line marked on the tank or on the manual. Reinstall the valve, open both valves, and run the filter on backwash for 3 to 5 minutes, then rinse for 1 minute. This flushes out fine dust from the new sand. After that, set the valve back to filter and you are done.

FAQs

Can you use any sand in a pool filter?

No. Only #20 grade silica pool filter sand, or a pool grade glass or zeolite alternative, belongs in a pool filter. Play sand, paver sand, quikrete, construction sand, and beach sand all fail in different ways. Play sand clogs the laterals. Construction sand clouds the water. Quikrete can react with pool chemistry. Use only media labeled specifically for pool filters.

Is pool filter sand different from regular sand?

Yes, in three specific ways. Filter sand is sized tightly between 0.45 and 0.55 mm. Its grains are angular and sharp-edged, not round like play sand. And it is washed and screened to remove clay, silt, and organic matter so it does not react with pool chemistry. Regular sand fails on at least one and usually all three of these points.

What kind of sand does an Intex pool filter use?

An Intex sand filter pump uses the same #20 grade silica sand as any other residential sand filter. The capacity is smaller, usually 45 to 55 pounds depending on the Intex model, but the specification is identical. Check your Intex manual for the exact amount, then buy standard #20 silica pool filter sand. Do not use Intex-branded sand as a required product. Any pool grade #20 silica works.

Can I mix old and new sand when refilling my filter?

No. Replace all of it. Old sand that has lost its angular edges will not suddenly start working again because fresh sand is above it, and a mixed bed settles unevenly, which can create channels that let water bypass filtration entirely. Dump the old, rinse the tank, and pour a full new load.

Do I need pea gravel under the sand?

Only if the manufacturer specifies it. Most modern residential sand filters do not need pea gravel and work best with sand only. Some older or larger commercial filters do use a gravel base layer under the sand. Check your filter's manual before adding anything besides sand.