Pool Filter Maintenance Guide: Sand, Cartridge, and DE Filters

Sand Filters: Backwashing Protocols and Media Replacement

Sand filters work by passing pool water through a bed of filter sand, typically #20 silica sand, where debris and particles are trapped in the spaces between sand grains. Over time, the accumulated debris increases filter resistance, which shows up as a rising pressure gauge reading. Most manufacturers recommend backwashing when the pressure gauge reads 8 to 10 PSI above the clean starting pressure. During a backwash, water flow through the filter is reversed, flushing captured debris out through the waste line. A proper backwash runs until the sight glass or waste water runs clear, typically 2 to 3 minutes. After backwashing, always run the filter in the rinse setting for 30 to 60 seconds to resettle the sand before returning to the filter position. Skipping the rinse step can allow loosened sand to return to the pool. Backwashing is not a substitute for periodic deep cleaning. Sand filters should be cleaned with a filter cleaner product once or twice per season to remove oils, calcium scale, and biofilm that backwashing doesn't fully eliminate. Pour the cleaner into the skimmer with the pump running, let it circulate, then backwash thoroughly after the recommended soak time. Sand media doesn't last forever. After 5 to 7 years of use, filter sand develops channeling, where water finds paths of least resistance through the bed rather than distributing evenly, which reduces filtration efficiency. When a pool's water clarity declines despite proper chemistry and backwashing, aged sand is often the cause. Sand replacement involves shutting the system down, manually removing the old sand with a wet vac or scoop, inspecting the laterals at the base of the filter for cracks, and refilling with fresh sand to the manufacturer's specified level. This is a service that adds real value and generates meaningful revenue, typically priced at $150 to $350 depending on filter size and your local market.

Cartridge Filters: Cleaning Procedures and Replacement Intervals

Cartridge filters use pleated polyester filter elements to capture debris and particles as water passes through them. They don't backwash; instead, the cartridges are periodically removed and cleaned manually. Cleaning frequency depends on bather load, pool usage, and the size of the cartridge relative to the pool. A general guideline is to inspect cartridges every 4 to 6 weeks and clean when pressure has risen 8 to 10 PSI above baseline or when the cartridges are visibly loaded with debris. To clean cartridges, shut off the pump, release any pressure in the canister by opening the air relief valve, and remove the filter lid. Lift out the cartridge or cartridges, take them to a suitable cleaning area, and rinse thoroughly with a garden hose using a straight-stream nozzle. Work from the top of the pleats downward, rinsing between each pleat fold to dislodge debris. Never use a pressure washer, which can damage the filter fabric and reduce filtration performance. For a deeper clean, soak cartridges in a filter cleaning solution for 8 to 12 hours to break down oils, sunscreen residue, and calcium deposits that rinsing alone won't remove. This soak-and-rinse method is recommended at least twice per season for pools with regular use. Inspect the cartridges after cleaning for torn fabric, collapsed end caps, or worn sealing rings. Damaged cartridges should be replaced immediately, as they allow unfiltered water to bypass the media and return to the pool. Cartridge life varies by manufacturer, usage, and how well they're maintained, but most residential cartridges are due for replacement every 1 to 3 years. Some operators offer a cartridge replacement program where they track the age of each client's cartridges and proactively recommend replacement, which reduces callbacks and demonstrates professionalism.

DE Filters: How They Work and How to Service Them

Diatomaceous earth filters provide the finest filtration of any filter type, capable of removing particles as small as 2 to 5 microns. They work by coating a set of internal grids with DE powder, which creates a highly porous filtering surface. Water passes through the DE-coated grids, and particles are captured in the DE layer. DE filters produce exceptionally clear water, which is why they're popular in high-end residential pools and commercial environments where water clarity is a priority. DE filters are backwashed similarly to sand filters, but there's an important additional step: after backwashing, DE powder must be added back to the filter to recoat the grids. The amount of DE to add depends on the filter's square footage as specified by the manufacturer, typically measured in pounds. Add DE by premixing it with water in a bucket to form a slurry, then pour it into the skimmer with the pump running so it gets drawn into the filter and deposits on the grids. Using too little DE leaves the grids exposed and reduces filtration quality. Using too much can cause the grids to stick together and restrict flow. Beyond routine backwashing, DE filters require a full disassembly cleaning at least once per season. This involves opening the tank, removing the internal grid assembly, disassembling the individual grids, and hosing each one down thoroughly to remove all accumulated DE and debris. Inspect grids for tears, which appear as small holes or splits in the fabric. A torn grid allows DE powder and unfiltered water to pass back into the pool, which shows up as a white or cloudy haze in the water. Torn grids must be replaced. Reassemble the filter, add fresh DE, and document the cleaning in your service record. DE filter service is a labor-intensive job that justifies a higher service price, typically $150 to $300 depending on filter size and your market rate.

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