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Why Change Your Pool Filter Sand?

The pool pump pulls dirty water to the filter, where it passes through the sand, where contaminants get trapped. The clean water flows back into the pool. How exactly does the sand hold onto the icky stuff, while allowing the cleaned water to pass through?

Though it’s much too small to see with the naked eye, all three types of sand have a rough surface where contaminants get caught as the water flows past.

Over time, the rushing water wears away the prickly surface of the sand, leaving it smooth and round. When you look at sand from beaches with intense waves under a microscope, it’s noticeably smoother than sand from calmer beaches. The same principle applies to pool filter sand, which has water flushed through it for several hours a day.

This smoothing is the result of a process called weathering. Ironically the same process that creates sand also wears it down into dust, useless for filtering anything.

When pool filter sand is weathered smooth, it doesn’t have any jagged edges to grab and hold contaminants. Your pool may start to look cloudy or require more frequent shock treatment as the filter media nears the end of its lifespan.

What is Pool Filter Sand?

Dead bugs. Bacteria. Algae. Your pool filter traps these things so they can’t hang around making the water cloudy or getting swimmers sick. The filter media is the stuff that grabs those contaminants. In this case, sand is that media.

Sand is such excellent filtration media, it’s used in other water safety applications such as wastewater treatment, septic systems, and even for drinking water.

To the untrained eye, most sand looks pretty much the same, so you might think all sand is created equal, but that’s not the case. Don’t be tempted by that bag of cheap play sand in your garage. It will destroy your filtration system. Always make sure to use one of three types of sand in your pool filter.

Silica Sand

The most commonly used pool filter sand is #20 silica sand. It comes from ground quartz, which creates sharp silica grains with jagged edges excellent for trapping particulates from passing water.

When to Change the Sand in Your Filter

Like fine wine, pool filter sand gets better with age, but then it peaks and eventually declines. Its lifespan is rather short—just three to five years. Over the course of a few years, contaminants build up in the sand.

For the first couple of years, this actually enhances the filtering ability of the sand because in addition the sand’s own rough edges, the contaminants building up also act as filtration for the water that passes through the filter.

But eventually, all that extra gunk builds up so much that it makes the filter prone to clogs. At the same time, weathering renders the sand incapable of collecting more contaminants. Your filter’s efficiency drops, and your pools water quality suffers.

Two other things may happen when your sand is past its peak. Pressure can build up inside your filter as it becomes more difficult for the water to pass through gunked-up sand. Then the water may seek a path of least resistance and cut a channel through the sand, which may reduce some of the pressure, but will virtually eliminate filtering.

Can’t I just Clean or Backwash my Sand Filter?

You’ll need to backwash your sand filter whenever the pressure gauge climbs to 10 pounds per square inch (psi) higher than the normal running pressure. You can also backwash if the water is a bit cloudy, but the chemistry is okay.

Backwashing rinses the sand, flushing debris to waste. It can be done as part of your routine pool maintenance, and you may need to top off the pool afterward, but eventually the sand will wear down and need to be replaced. If your sand is in the three- to five-year window, and pressure and clarity are ongoing problems, it’s probably time for new sand.

By: Poolice Officer
In: Pool Equipment, Pool Filter, Pool Filter Sand
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Poolice Officer