Pool filters come in three types — sand, cartridge, and diatomaceous earth (DE) — and each works differently, requires different maintenance, and performs to a different standard. Understanding which type you have and how to maintain it correctly is fundamental to keeping your pool water clear and your pump running efficiently.
Sand filters
Sand filters are the most common type in residential pools. They use a tank filled with #20 silica sand (or an alternative media like glass or zeolite) to trap particles as water passes through. Water enters from the top, flows through the sand bed, and exits clean through the laterals at the bottom.
Filtration capability: Sand filters trap particles down to approximately 20–40 microns. They're the least fine of the three filter types — adequate for most pools but not the best choice for pools that need very clear water or have fine particle issues.
Maintenance: Sand filters are cleaned by backwashing — reversing the flow of water through the tank to flush debris out through the waste line. Backwash when the filter pressure gauge reads 8–10 PSI above the clean starting pressure (note your clean pressure after installation or after a full cleaning). Backwash takes 2–3 minutes and should be followed by a brief "rinse" cycle to reseat the sand before returning to filter mode.
Media replacement: Sand doesn't last forever — it becomes coated with oils, mineral deposits, and debris that backwashing can't remove, reducing filtration effectiveness. Replace the sand every 5–7 years or when you notice the pool isn't clearing properly despite adequate chemistry and backwashing. Some pools benefit from alternative media: glass media (finer filtration, lasts longer) or zeolite (binds ammonia compounds, good for high-bather-load pools).
Best for: Larger pools, pools in debris-heavy environments (open pools with trees), and situations where ease of maintenance is a priority. Backwashing is quick and doesn't require the filter to be opened.
Cartridge filters
Cartridge filters use pleated polyester filter elements — similar in concept to an air filter in a car — to trap debris. Water flows from outside to inside the cartridge element, and particles are trapped in the pleated material.
Filtration capability: Cartridge filters typically filter to 10–15 microns — finer than sand, producing clearer water. They're the most common filter type for smaller to mid-size residential pools in Florida.
Maintenance: Cartridge filters don't backwash — they're cleaned by removing the cartridge element(s) and rinsing with a garden hose, working from top to bottom between the pleats. Clean when pressure rises 8–10 PSI above the clean operating pressure. For a thorough clean (monthly or as needed), soak the cartridge in a cartridge cleaning solution overnight to remove oils and mineral deposits that rinsing doesn't reach.
Cartridge replacement: Replace cartridges when they show visible damage (torn or collapsed pleats, deteriorating end caps), when they don't return to normal pressure after cleaning, or approximately every 2–3 years under regular service. A cartridge that's past its life reduces filtration efficiency and puts strain on the pump.
Best for: Mid-size residential pools, screened pools with lighter debris loads, and situations where water conservation matters (cartridge filters don't require backwashing, which wastes water). Not ideal for heavy leaf and debris loads — cartridges clog faster under those conditions.
Diatomaceous earth (DE) filters
DE filters use grids or fingers coated with diatomaceous earth — a powder made from fossilized algae — as the filter medium. The microscopic structure of DE traps particles at an extremely fine level as water passes through the coated grids.
Filtration capability: DE filters filter to 2–5 microns — the finest of the three types, producing noticeably clearer water. In a well-maintained DE filter, the difference in water clarity compared to sand is visible.
Maintenance: DE filters can be backwashed (though this is less efficient than with sand — some DE is lost with each backwash and must be replenished by adding new DE through the skimmer). For a full cleaning, the filter is opened, the grids are removed and cleaned thoroughly, and fresh DE is added after reassembly. This full breakdown cleaning should be done 1–2 times per year.
Handling DE: Diatomaceous earth is a fine powder that should be handled with care — avoid inhaling it. Mix with water before adding to the skimmer rather than adding it dry. Store in a dry location in a sealed container.
Best for: Pools where water clarity is a priority, smaller pools, and pool owners who are committed to the additional maintenance complexity DE requires. Not the best choice for heavily debris-laden pools due to the faster clogging and more involved cleaning process.
Choosing a filter type
If you're replacing a filter, the choice depends on your pool's needs:
- Open pool with heavy debris, prioritize maintenance simplicity → sand
- Screened pool, moderate debris, want better clarity → cartridge
- Clear water is the priority, willing to do more involved maintenance → DE
For most residential pools in the Tampa Bay area, cartridge is the right default — it provides good filtration, doesn't waste water, and is straightforward to maintain with regular cleaning.