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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.
Pool filters are as important to your pool as your kidneys are to your own body. We know that sounds kind of gross, but it’s true. Though chlorine and other sanitizers work to kill bacteria and other contaminants, the filter is what actually removes them from the water. Without it, your pool water would grow cloudy and fill with debris. Not exactly fun for swimming.
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. So don’t go sprinkling that pest-control powder into your pool filter when you run out of D.E., mm-kay? We’re talking about different kinds of pests here.
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 as small as 10 microns 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.
Whether they’ve been killed by chlorine or not, bacteria and other contaminants can only be filtered out if the filter media—the material that actually does the filtering—is fine enough to collect those teeny, tiny particles.
The first step to choosing the best 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.
But before you can accurately compare pool filter types, how well they function, and how much work they require to maintain, you need to know about microns.
WHAT IS A MICRON?
Pool filters measure the size of contaminants they’re capable of removing in microns. It’s short for micrometer, which is one millionth of a meter.
Having trouble picturing just how small that is? A single strand of human hair is about 50 microns, or about .05 millimeters in diameter. Some bacteria measures about 2 microns, or about .002 millimeters in diameter.
Filters are rated by gallons per minute (GPM) per square foot. The filter flow rate must be rated at least the same GPM as your pump, or higher. With pool filters, it’s best to err on the larger size so it can handle the power of your pump. A helpful rule of thumb is to choose a filter with at least 1 square foot per 10,000 gallons pool capacity.
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 pass through the filter.
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 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 waste.
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.