What Type of Sand for Pool Filter? — #20 Silica vs Alternatives

The Only Correct Answer: #20 Grade Silica Sand

The correct pool filter sand is #20 grade silica sand with a grain size of 0.45–0.55 mm.

It is sold as “pool filter sand,” “#20 silica sand,” or sometimes “pool sand” at pool supply stores, home improvement stores, and online. It is bright white, loose-grained, and specifically graded for pool filtration.

Everything else — play sand, construction sand, river sand, beach sand — is the wrong answer. Here is exactly why grain size matters, and what happens if you use the wrong media.

Why Grain Size Is Everything

Pool filter sand works by mechanical filtration: pool water passes down through a tightly packed bed of sand grains, and debris too large to pass through the gaps gets trapped.

The gap size between grains determines what gets trapped vs. what passes through:

• Too fine (< 0.35 mm): Grains slip through the laterals (the plastic slots at the bottom of the tank). Result: cloudy white water in the pool, clogged laterals, possibly damaged laterals.
• Too coarse (> 0.65 mm): Gaps between grains are too large. Debris passes through unfiltered. Result: dirty pool water despite the filter running.
• Correct (0.45–0.55 mm): Grains stay above the laterals, gaps are sized to trap particles 20 microns and larger.

The #20 grade designation refers to U.S. sieve size #20 — meaning 95%+ of grains fall within this size range. Processed pool filter sand is quality-controlled to this specification. Random sand from a sandbox or building site is not.

Can You Use Play Sand? No — Here’s What Happens

Play sand is the most common wrong choice, so it deserves a specific answer.

When you fill a pool filter with play sand and turn on the pump, within minutes you will see white, milky water coming out of the return jets. This is fine sand and silica dust passing straight through the filter laterals into the pool.

Play sand grain size is typically 0.1–0.3 mm — too fine for pool filter laterals. The laterals are slotted openings sized to retain #20 grade sand while allowing water to pass. Finer sand particles slip through these slots freely.

Additionally, play sand contains organic material, clay particles, and inconsistently-sized grains. None of these belong in a pool filter.

The fix requires draining and refilling the filter with the correct sand — and cleaning the pool of the white haze. Avoidable entirely by buying the right product.

Sand Alternatives: When to Consider an Upgrade

ZeoSand (Zeolite Mineral Media)

ZeoSand is a natural zeolite mineral that replaces pool filter sand in the same tank.

ZeoSand is a worthwhile upgrade for pools with high bather loads, persistent clarity issues, or where eye irritation (from chloramines) is a problem. For lightly-used backyard pools, standard silica sand delivers excellent results.

Pool Filter Glass (Recycled Glass Media)

Pool filter glass is crushed recycled glass with a grain size of 0.5–1.0 mm. It provides filtration down to approximately 3 microns — finer than ZeoSand.

Filter glass is the longest-lasting option and its smooth surface resists biofilm (the bacterial layer that grows on silica sand over time). It lasts longer per tank and provides the finest filtration of any sand-type media. For pool owners who want to set and forget, filter glass is the most low-maintenance option.

Pool Filter Balls

Pool filter balls are polyester fibre balls that replace sand. They are reusable and claim to filter down to 3 microns.

Real-world performance is mixed — they work well when new but lose effectiveness faster than sand and require more frequent cleaning. See our full filter type comparison for more on alternative filter media.

Which Sand Brand to Buy

For standard #20 silica sand, look for brands specifically labeled as “pool filter sand.” Our best pool filter sand review covers the top brands we have sieve-tested — not all pool filter sand is equally consistent in grain size.

HTH #20 Pool Filter Sand and Fairmount Minerals are the two brands we found most consistent in grain size testing. Both are available at major retailers and online.

How Much Do You Need?

See our how much sand for pool filter size chart for the exact quantity by tank diameter and popular filter models. A 24-inch tank (the most common residential size) needs 200 lbs — four 50 lb bags.

Related Guides

• How Much Sand for Pool Filter? — exact quantities by tank size
• How to Change Pool Filter Sand — full replacement procedure
• Best Pool Filter Sand — tested brands ranked
• Sand Filter Complete Guide — all sand filter topics