Running a sand filter empty: what actually happens
The sand is the filter — it's the bed that traps dirt as water passes through. With no media, water flows straight through the laterals and back to the pool unfiltered, and the fine debris that should be caught gets returned. Nothing dramatic happens to the pump mechanically (filter media isn't a lubricant), but you've effectively switched your filtration off. Treat an empty tank as "fix it soon," not a way to run.
Before you open the tank: shut off the pump, set the multiport valve to "closed" or "winterize," and release system pressure with the air-relief valve.
Standard refill: pool-grade #20 silica sand
The default media is #20 pool-grade silica sand, which traps particles down to about 20-40 microns. It's cheap, reliable, lasts roughly 5-7 years (often longer), and is what most sand filters are built around. If you just want your filter working again, this is the simplest answer.
Sand alternatives that drop into the same tank
Filter glass
Recycled glass media filters finer than sand — down to about 5-10 microns — and you use roughly 20% less by weight. It resists channeling and can last up to 10 years, which makes it a popular upgrade.
Zeolite (ZeoSand)
A natural mineral media that filters finer than sand and also absorbs ammonia (chloramines), which can help with chlorine smell and water quality. It's lighter, too — roughly 50 pounds of zeolite replaces 100 pounds of sand.
Filter balls
Lightweight polyethylene-fiber spheres, by far the easiest to handle (a small bag replaces a 50-pound bag of sand). They're convenient, but real-world filtration reports are mixed, and owners generally replace them sooner than sand (commonly every 1-3 years). See our filter balls vs. sand guide for the full tradeoffs.
Or skip sand entirely: different filter types
If you're rethinking the whole setup, the two non-sand filter types are cartridge filters (pleated elements, ~10-20 microns, no backwashing) and DE filters (diatomaceous earth, the finest at ~1-5 microns). These aren't drop-in media swaps — they're different equipment — but they're worth knowing if you want finer filtration.
Matching media to your filter
- Follow your filter's manufacturer guidance for the correct media type and amount.
- Don't mix media types in one tank.
- Filter balls aren't backwashed the same way as sand — check the product instructions.
- Dispose of old media according to local regulations.
