Swimming Pool Filters

Pool filters are the most important piece of equipment your pool has.  Though chlorine and other sanitizers work to kill bacteria and other contaminants, the filter is what mechanically removes them from the water. Without it, your pool water would grow cloudy and fill with debris. So how do you choose the best one? It’s not about which one is the least expensive, though cost is certainly a factor. You want a filter that will trap contaminants, be easy to clean and maintain, and last more than just a few seasons. In order to make the best selection for your pool, first get a handle on your options. If you’re choosing between a sand filter, a cartridge filter or a DE filter, a lot of your choice will boil down to how much money and maintenance time you want to put into filtering your pool’s water. You should also consider how important it is for you to have extremely clean pool water.

Types of Swimming Pool Filters

The first step to choosing the best pool filter is knowing what your options are. You have three types of filters to choose from: sand, cartridge, and diatomaceous earth, or D.E. Price, replacement frequency, and filtration rates differ by type. And if you’re wondering how to clean a pool filter, that will also depend on the type you select.

If you’re on a budget, and you want to spend minimal time on maintenance, a sand filter is the best choice for you. It’s also optimal for large pools because it won’t clog as easily as other filters.

Your pool pump sucks water in from the skimmers, then pushes it through a large filtration tank full of sand. The standard media used inside the tank is #20 silica sand. It grabs particles that measure 20 microns and larger.

Each grain of sand is, for lack of a better word, prickly. If you could look at it under a microscope, you’d see it has lots of little rough edges all around it, which is how it grabs contaminants and debris that come into the filter from the pump.

As weeks and years pass, and more water flows through the filter, those rough edges are slowly worn down by erosion, eventually becoming smooth surfaces that aren’t able to capture anything.

At the same time, the particles trapped within the sand will build up over the life of the filter. This can actually help trap smaller particles, even as the sand itself begins to smooth out. But eventually, it will prevent proper water flow through the filter, reducing the filter’s efficiency.

A pressure gauge on the side or on top of the filter will alert you to increasing internal pressure—a sign it’s time to backwash the filter. This easy cleaning method the filter reverses the water flow, flushing all the debris to a waste line and essentially flushes the sand.

Because the silica captures particles of 20 microns or larger, you’ll really need to stay on top of your pool water chemistry. If there’s not enough sanitizer in your pool to kill those tiny, 2-micron bacteria, a sand filter isn’t going to catch them either, and they’ll be floating around in your pool with you.

Sand Filter Pros:

  • Lower cost
  • Easier maintenance
  • Sand lasts five to seven years before needing to be changed
  • Filtration efficiency can be boosted with additives alternative media

Sand Filter Cons:

  • 20-micron filtration is the least effective of the three types
  • Backwashing and rinsing wastes water
  • Building pressure decreases filter efficiency
Though they’re typically a bit more expensive than sand filters, cartridge filters are just as easy to maintain, and are more effective as long as you don’t have a huge pool. Inside a tank slightly smaller than their sand cousins is a plastic cylinder surrounded by pleated polyester filter media and capped on each end. Water flows into the tank and through the pleats. Debris is captured in the filter, then clean water heads back to the pool. Cartridges are energy efficient and inexpensive. As the filter collects contaminants, it’ll need cleaning. Rather than backwashing, you’ll simply remove the cartridge from the tank, and spray it with a hose to remove debris and dirt. Occasionally, you’ll want to spray it down with filter cleaner, and on a regular basis, soak it in diluted muriatic acid or a chemical filter cleaning solution. While this is a bit more physical work for you than backwashing, it wastes less water.

Cartridge Filter Pros:

  • Filters contaminants as small as 10 microns
  • No backwashing; less water waste
  • Performs well at low speeds, such as with variable-speed pumps

Cartridge Filter Cons:

  • More work than sand filters
  • Lasts only 2 to 3 years
  • Deep cleaning required 1 to 2 times per year
The most expensive, maintenance-intensive option also happens to filter the smallest particles of all three types of filters: 5 microns. D.E. filter tanks contain grids or “fingers” covered in the crumbly, white powder. The powder is made from the crushed fossilized remains of tiny, aquatic organisms called diatoms. Though D.E. and sand pool filters are different, the fossils in D.E. are also composed of silica. The powdery substance can be found in pest control, cosmetics, and even toothpastes, but D.E. made for pool filters is heat-treated to work as a filtration media.

Backwash or Bump Cleaning

Like sand filters, a pressure gauge on the tank will let you know when it’s time to clean your D.E. filter. Typically, D.E. filters are backwashed just like sand filters. Some brands feature a bump handle, which lets you knock the used D.E. off the grids or fingers to clean. Whether you backwash or bump the filter, you’ll need to add more D.E. powder after every cleaning. It can be difficult to determine exactly how much to add, so it’s especially important to disassemble and clean the filter by hand at least once a year.

How to Add New D.E. to the Filter

After you’ve cleaned your filter, rather than adding D.E. powder directly to the grids, you’ll get much better coverage if you add it through the pool’s skimmer.
  • Mix the D.E with enough water to make a slurry, which will look like a thin, creamy solution.
  • Make sure the pool pump is running.
  • Slowly pour the solution directly into the skimmer.
As the D.E. passes through the filter, it will evenly distribute over the grids. You’ll need to wait a while before swimming to give the mixture time to fully integrate with the filter, so you may want to do this in the evening, and then run your pump overnight.

D.E. Filter Pros:

  • Filters contaminants as small as 5 microns
  • D.E. powder can be added through the pool skimmer
  • No caustic chemicals are required for cleaning

D.E. Filter Cons:

  • Highest cost filter
  • Annual cleaning is a lot of work
  • Grids need replacement every 2 to 3 years
  • Hard to find for above ground pools
  • Backwashing may be restricted by locale
  • D.E. powder can be harmful if inhaled