Sand vs. Glass vs. Filter Balls: What to Put in Your Sand Filter

Here’s the thing most owners don’t realize: a “sand filter” is really just a tank you fill with a filtering medium — and sand is only one option. The same tank will run recycled glass or poly-fiber filter balls, and the choice changes how clean your water gets, how often you replace it, and how much you have to lift. (Still deciding whether to run a sand filter at all, versus a cartridge? Settle that first with our sand vs cartridge guide.)

How a sand filter actually cleans

Water gets pushed down through a bed of media; dirt and debris get caught in the gaps between the particles while clean water passes through and returns to the pool. Over time the trapped gunk fills those gaps, pressure rises, and you backwash — reverse the flow to flush the dirt out to waste. The media itself just needs to be the right size and shape to trap fine particles without choking off the flow. That’s why the medium you choose matters.

The three media, honestly

• Traditional sand (#20 silica) — the safe default. Cheapest to buy, filters to about 20–40 microns, lasts 3–5 years, and it’s heavy (a filter can take 100–300 lb). It works fine and it’s foolproof. Its weakness: over years the grains wear smooth and the bed channels, so filtration quietly gets worse until you replace it.
• Recycled glass — the upgrade most people should make. Crushed, sized glass that drops into the same tank and filters finer (~10–15 microns), lasts longer (~5–7+ years), and weighs about 20% less for the same job. Its slight negative surface charge helps grab fine particles and resists channeling. It costs more up front and that’s the whole downside.
• Poly-fiber filter balls — the lightweight wildcard. Astonishingly light (a pound can replace 50–100 lb of sand), cheap, washable and reusable, and fine on paper (makers claim as fine as ~5 microns). But quality varies wildly: cheap balls mat down, channel, and clog, they can be hard to backwash well, and lesser ones shed fibers. Good for a small, lightly used above-ground pool if you buy well-reviewed ones — riskier for anything working hard.

How to choose

What to actually buy

Commodity media rank on two things: the grade your filter’s maker specifies, and the price per pound. Star ratings on a bag of sand mostly measure the delivery, so we don’t rank on them.

The grade rule, before any brand

Both big sand-filter makers name one grade, and it’s the same one. Hayward’s sand filter manual: “Use only High Rate Sand No. 20 Silica Sand (.45mm-.55mm).” Pentair’s Sand Dollar and Cristal-Flo II guide: “You must use only No. 20 standard silica sand having a uniformity coefficient of 1.75 or less. No. 20 silica sand has a particle size of .018-.022 inches (.45 to .55 mm).”

That grain size is what the slots in your filter’s laterals are built around. Sand finer than #20 passes straight through them and lands on your pool floor, every run, and no amount of backwashing stops it. It is also the single most common complaint on the sand we read online — which is why a listing that states the grade is worth more than one with a higher star average.

Wear an N95 or better while you pour. Silica sand is crystalline silica and its dust is respirable; glass throws dust too. Pour slowly, outdoors, with the filter half full of water so the media settles rather than clouds.

Sand: buy #20 locally first

This is the one where mail order makes the least sense. A 50 lb bag of #20 silica runs $12–20 at a pool or hardware store, you need several, and you can read the grade on the bag before you carry it out. Heavy and cheap is the worst possible combination for shipping.

If you have to buy sand online

Every online sand we read in September 2026 shipped from the same marketplace seller, and every one of them carries torn-bag complaints. Open each bag on delivery and look at the grains before any of it goes in the tank. These are the three worth considering, in order.

It’s the only one that says #20 up front, with a grain size — and its own critical tail disputes it. A 2026 owner calls it “play sand” with “grains the same size as table salt,” and two 2025 owners report sand coming out of the pump head, which is exactly the too-fine failure the grade is supposed to rule out. That is a minority on 4.5★ across 331 ratings, but look at the grains.

It states no grade at all — “pre-washed, kiln-dried natural silica” is all the listing says. Its 2026 reviews are about the bag more than the filtering: bags split in the box, sand that arrived brown rather than white, and tree bark in one bag. Its rating is pooled with a 20 lb bag.

The deepest record, and a repeated too-fine theme inside it. From 2023 to 2025 owners describe sand “way way way too fine for sand pumps” that took three or four vacuum sessions to clear from the pool. On 4.7★ across 2,911 ratings that’s a small share, but it is the grade problem again. The listing mentions “20# Grade” only in its detail table, and U.S. Silica’s own page says Mystic White II comes in several sizes, #20 among them — so look at the grains on this one too.

Two we read and didn’t card. Palmetto has a deep rating but had no buy box when we read it — no price, no seller — and its 2026 reviews include an order that shipped bags of play sand, plus a 2025 owner whose sand was “too small of grain” and went through the baffles. OptiFlow is sold by the same seller at a similar price and its listing states no grade.

Glass: the upgrade

Glass replaces sand at about 80% by weight. Vitroclean, a recycled-glass media maker, puts it as “40 lbs of Vitroclean replaces 50 lbs. of sand” — multiply your filter’s sand weight by 0.8. That’s a maker claim, and a zeolite maker’s brochure repeats the same 80% figure for glass. So a tank that takes 150 lb of sand wants about 120 lb of glass: price the whole job, not the bag.

One honest caveat before you buy it: the Amazon listing states no micron rating, and the business behind the bag has changed hands. The glass is now made by Reed Minerals, which sells it as BrightLine and claims it removes particles as fine as 5 microns, with a .52–.72 mm grain. That is the maker’s claim, not a test — and the ~10–15 micron figure quoted for glass media elsewhere in this guide is a claim about the category. It’s a real upgrade over worn sand; it just isn’t a measured one.

And a second one, which is more serious. The critical tail on this bag is small — 19 reviews at our September 2026 read, on 4.7★ across 605 ratings — but it is coherent, and it goes at the core claim: seven of the ten we read in August were owners who swapped sand for this glass and could not keep the water clear until they swapped back. These are not careless reports. One dye-tested that water was genuinely flowing through the media and found the backwash running clear while the pool stayed green. Another covered the pool to rule out debris blowing in, and still found dirt on the floor. A third pulled known-good five-year-old sand out of a Hayward filter to make room for it. That is a minority and we have kept the pick — but the failure mode is invisible: your chemistry reads perfect, your filter looks fine, and the water simply never clears.

It now has 2026 reports too — we said in August that it didn’t. Our earlier read found those complaints spread across 2019, 2022, 2023 and 2025 and nothing in 2026. The September re-read adds an owner whose pool “turned green within a week” (August 2026), plus two complaints about the seller — a refund that took over a month and a short order. One new filtering report isn’t a batch gone bad, and the pick holds, but it is no longer true that nothing has been reported this season. The rating also slipped a tenth of a star on a dozen new reviews.

If your water won’t clear on good chemistry, suspect the media before you spend another month on chemicals. A local bag of #20 is cheap, and going back is cheap.

What a full fill actually costs

Prices are the September 2026 reads, per pound, computed from the bag price. The sand column assumes a filter that takes 150 lb or 100 lb of sand; glass is figured at 80% of that weight.

You buy whole bags, so round up: 120 lb of glass is three 40 lb bags, and 150 lb of sand is three 50 lb bags. Your filter’s own label or manual gives its sand weight — use that, not a guess from the tank diameter.

Filter balls

Filter balls — we’re not naming one, and that’s the finding. Every ball on the shelf is the same shape of product sold on the same weight claim — “3.5 lbs replaces 100 lbs of sand,” “5.5 lbs replaces 250 lbs” — with no consistent spec between them and every sign of being one or two moulds under a dozen brand names. Since the whole known problem with filter balls is that quality varies wildly, recommending one of a set we can’t tell apart would be worse than recommending none. If you want to try them on a small above-ground pool, buy the best-reviewed one you can find, follow the maker’s fill weight, and don’t pack the tank.

The honest bottom line

The medium in your sand filter is a real, cheap upgrade lever — glass genuinely filters finer and lasts longer than sand, and it’s the swap most owners should make next time the bed is due. Filter balls are a legitimate lightweight option for the right (small, light-load) pool, just hold the quality bar high and don’t overpack. But no medium is magic: if the water’s still cloudy, the filter is usually the last suspect, not the first — check your chlorine and balance before you blame the sand. That’s the same less-is-more idea: fix the water, and the filter’s job gets easy. And if the filter itself is undersized or worn out — not the medium — that’s a hardware fix, not a media swap: see our picks for above-ground sand filter systems and, if you’re still deciding on the type, sand vs. cartridge.