The modern swimming pool is a complex hydraulic system, but if the pump is the muscle, the filtration unit is the “Hydraulic Heart.” While sanitation systems (like chlorine or salt generators) are responsible for killing pathogens, the filter is tasked with the physical removal of debris, suspended solids, and organic matter.
Without effective filtration, the efficacy of your chemical sanitizers is compromised. Turbidity (cloudy water) shields bacteria from disinfection, increases chemical demand, and ruins the aesthetic appeal of the water. Whether you are a homeowner or a service professional, understanding the physics of your specific filter type is the key to maintaining a safe and sparkling pool.
To understand filtration, one must understand the “micron rating”—a measurement of the smallest particle size a filter can reliably capture. For context, the human eye can see particles roughly 40 microns and larger, while a human hair is approximately 70 microns in diameter.
Sand filtration is the oldest technology in pool water treatment, yet it remains the “workhorse” of the industry, particularly in commercial settings and regions with heavy organic debris.
Sand filters utilize “depth filtration.” Water is driven into a pressurized tank and dispersed across a bed of #20 silica sand. As water navigates the jagged edges of the sand grains, debris is trapped in the spaces between them.
Unlike other filters that require disassembly, sand filters are cleaned hydraulically. When the internal pressure rises 8–10 PSI above the clean starting pressure, the operator reverses the flow (backwashing) to flush the trapped debris out of a waste line.
For better performance, many professionals are switching from silica sand to recycled crushed glass. Glass media filters down to 5–9 microns, resists bacterial bio-fouling, and uses approximately 23% less water during backwashing.
Cartridge filters have become the dominant choice in water-scarce regions like the American West. They rely on “surface filtration,” trapping debris on the face of a pleated fabric membrane.
Water flows from the exterior of the cartridge to the hollow inner core. The pleats provide a massive surface area—often 300 to 500 square feet in “Quad” style units—which allows for long intervals between cleanings.
Cartridge systems do not have a backwash valve, which saves thousands of gallons of water annually. Cleaning requires physically removing the elements and washing them with a high-pressure hose.
DE filtration is widely regarded as the “gold standard” for water clarity, often producing “polished” or “sparkling” water.
This method uses “cake filtration.” The internal grids are coated with DE powder—microscopic fossilized exoskeletons of diatoms—which act as a sieve to catch particles as small as 2 microns.
Like sand filters, DE units are backwashed. However, because backwashing expels the DE powder, fresh powder must be added to the skimmer immediately to recoat the grids. Failure to recharge the filter will ruin the grid fabric.
Selecting the correct filtration system is not just a matter of preference; it is an engineering decision that balances hydraulic physics, regional environmental factors, and economic realities. Use this decision matrix to determine the best fit for your specific pool profile.
The “Low-Maintenance” Workhorse: Sand Filtration
Black algae is a type of bacteria that can be really tough to kill and control in your pool. Here we show you had to kill black algae fast and how to prevent it from coming back.
If you live an area where the weather gets cold during the winter, then you’ll need to close your pool. Here we give you a step-by-step guide on how to do it right. And make sure your pool opening will be a breeze in the spring.
