Sand vs. cartridge vs. DE pool filters: how they compare
All three filter types do the same job: trap the particles that make water dull or cloudy. They differ in how fine they filter, how they're cleaned and how much attention they need. Clear water depends first on chlorine and pH, so any properly sized, clean filter can keep a well-balanced pool sparkling.
At a glance
| Sand | Cartridge | DE (diatomaceous earth) | |
|---|---|---|---|
| Filtration | Coarsest of the three | Finer than sand | Finest |
| Cleaning | Backwash (reverse the flow to waste) | Remove and hose off the cartridges | Backwash or take apart, then add fresh DE powder |
| Water used to clean | Most (each backwash sends water to waste) | Least | Some, if it backwashes |
| Ongoing media | Replace sand every several years | Replace cartridges every few years | Add DE after each cleaning. Replace grids when worn. |
| Effort | Lowest | Moderate | Highest |
Sand filters
Water flows down through a bed of filter sand (or a glass or zeolite alternative), which traps particles. As dirt builds up, the pressure gauge rises. When it's about 8–10 psi above its clean reading, or as the manufacturer recommends, you backwash: reverse the flow to flush the dirt out to waste, then rinse.
- Pros: simple, durable, little hands-on cleaning.
- Cons: coarsest filtration, and backwashing wastes water, along with the salt and stabilizer in it. Sand clumps or channels over the years, so it needs replacing eventually.
- A clean sand filter actually filters a little less finely than a slightly dirty one, so don't backwash more often than you need to.
Cartridge filters
Water passes through pleated polyester cartridges. When pressure rises, you turn off the pump, take the cartridges out and hose them clean, and soak them in a cartridge cleaner now and then.
- Pros: finer filtration than sand, no backwash water lost, so salt and stabilizer stay in the pool. Low running pressure, which can help pump efficiency.
- Cons: cleaning is hands-on and messy. Cartridges wear out and cost money to replace.
- Larger cartridge area means longer between cleanings. Many owners size up for that reason.
DE filters
Grids or fingers inside the tank are coated with diatomaceous earth powder, which forms a very fine filter layer. After backwashing or cleaning, you add fresh DE through the skimmer to recoat the grids.
- Pros: the finest filtration, giving very polished water.
- Cons: most maintenance. DE powder is a fine dust: wear a dust mask when handling it, as product labels advise, and keep it out of the air. Some areas regulate how backwashed DE can be discharged. A torn grid sends DE into the pool, which shows as fine powder on the floor.
Which one should you choose?
- Least work: sand.
- Saltwater pools, or areas where water is scarce or expensive: cartridge, since there's no backwash to waste salt, stabilizer and water.
- Clearest possible water, and you don't mind the maintenance: DE.
- Replacing an existing filter: staying with the same type and connection size is usually simplest. Check that the new filter's maximum flow rate is above your pump's actual flow.
Sizing the filter
Every filter has a maximum flow rating. The pump's real flow should stay below it, and comfortably below for cartridges and DE. Check your flow needs with the pump turnover calculator. A filter rated close to the pump's flow clogs faster, needs more frequent cleaning and filters less well.
When the filter isn't the problem
If the water is cloudy, check free chlorine against your stabilizer level and pH before blaming the filter. Most cloudy pools are a chemistry problem first. See why is my pool cloudy. If chemistry is right and the water stays dull, look for damaged media, a stuck valve, too little run time or a filter that's too small.
Frequently asked questions
Can I add DE to a sand or cartridge filter?
Some owners add a small amount of DE to a sand filter after backwashing to improve filtration. Follow the filter maker's guidance. Don't add DE to cartridge filters unless the maker says so.
How often should I clean my filter?
When the pressure gauge reads about 8–10 psi above its clean starting pressure, or as the manufacturer recommends, rather than on a fixed schedule. Note the clean pressure each time so you have a baseline.
Do filters remove algae or germs?
Filters remove particles, including dead algae, but chlorine is what kills germs and algae. A filter can't make up for low chlorine.