Keep your pool filters free and clear   with regular maintenance

Keeping   the pool clean is a dirty job, which is why to clear dirt and debris   effectively, pool filters need periodic cleanings themselves.

The   three most common types of swimming pool filters are diatomaceous earth (DE),   sand and cartridge filters. Understanding how these different pool filters   work and how to maintain them can make your job easier, keep your pools   looking good, and keep your customers happy.

Micron   ratings

The   filter’s job is to trap all of the fine dust, dirt and sand particles that   pass through the skimmer basket and the hair-and-lint pot. Filters can make   the pool water look beautifully blue and crystal clear, but the water is not   necessarily pure. The misconception that a filter can purify water leads too   many homeowners and pool techs to blame cloudy water on filters instead of   proper water balance and sanitation.

Filters   remove only solid particles from swimming pool water. They generally cannot   remove dissolved contaminants, such as oils, bacteria or disease-causing   pathogens.

A   swimming pool filter’s efficiency is measured by its micron rating, meaning   how many microns can pass through the filter. A micron is a unit of length   equal to one millionth of a meter (1/1,000,000 m), or 0.0000394 of an inch.

A   grain of ordinary table salt is about 100 microns, and the human eye can see   down to about 35 microns without the aid of magnification. The lower the   micron rating on a pool filter, the smaller the particles it can remove from   the water.

Diatomaceous   Earth filters

The   DE filter is a favorite of pool builders and service technicians because it   has the best micron rating. A DE filter can strain out particles as small as 1   to 3 microns.

Diatomaceous   earth is a white powder that is made of the tiny skeletal remains of sea   creatures, called diatoms, which died prehistorically. Inside the DE filter   tank are eight semi-circular grids. The DE coats the grids and forms a filter   cake, which acts as a micro-screen to strain out tiny pieces of debris.

Pure   DE will not compact, so the pool water can easily pass through it. The dirt   and debris that is trapped in the filter cake will cause the filter cake to   pack and restrict water flow.

The   DE filter may be partially cleaned by backwashing. All DE filters have a   valve that allows the pool water to run backwards through the filter. Pool   water enters the filter and rinses most of the filter cake, dirt and debris   away to the sewer drain.

The   filter grids must be re-coated with a new filter cake after each backwashing.   Because backwashing does not remove all of the dirt and debris from the   filter, it is necessary to periodically open the filter and clean each grid   individually.

Separation   tanks

The   separation tank, found on many systems, is used to backwash a DE filter. The   job of the separation tank is to separate the DE and filter dirt from the   water while it is being backwashed.

Many   cities have banned DE and filter dirt from being backwashed down the street   and into storm drains. Some cities also don’t want DE and filter dirt   entering the sewer system, lest it clog the pipes. Therefore, during   backwashing, the discharged water must pass through a separation tank.

The   separation tank contains a strainer bag, which traps the DE dirt and muck.   Depending on the city ordinance, the clean, DE-free pool water is either   returned to the pool or sent down the sewer drains.

The   separation tank should be cleaned every time the filter is cleaned, and its   contents must be disposed of in a proper trash receptacle. It is important to   clean the separation tank at regular intervals — i.e., every time you clean   the filter — because the more impacted it gets, the less effective it   becomes; the heavier the strainer bag gets, the harder it is to remove; and   the more oils it collects, the worse its odor will be.

Adding   DE

After   backwashing the filter, you will need to add more DE to it through the   skimmer. Some pool techs will put the DE into a bucket, add water, then pour   the whole mixture down the skimmer; others will scoop the DE into the skimmer   directly.

DE   is added at a rate of 1 pound per 10 square feet of filter (always round up).   For years, a 1-pound coffee can was used as a DE measure; a 1-pound coffee   can holds 1/2 pound of DE, so you would use two 16-ounce coffee cans per   pound of DE. But coffee cans now hold only between 10 and 13 ounces — not 16   — so they are not recommended anymore. A 1-pound scoop is available at any   supply house. A 44-ounce drink cup also holds a pound of DE.

Sand   filters

A   sand filter is the oldest and simplest filter in use: The water used in the   famous Roman baths was filtered by running it through sand. The sand inside   the filter is called the sand bed. As the pool water passes through tiny   openings in the sand bed, dirt particles and other debris are trapped.

Sand   filters are virtually maintenance-free. A good sand filter can go years and   years on backwashing alone, if the backwashing is done right. There are no   grids to clean and no DE or sand to add — just backwash and go.

The   edges of the sand particles create tiny crevices to filter the water and   catch the debris. As dirt passes through the filter, it becomes trapped in   these crevices while the clean water passes through.

Just   as you would with a DE filter, when you backwash a sand filter, you run the   water backwards through the system so that all the dirt in the crevices and   gaps rises to the top of the filter and goes down the backwash line.

Sand   filters have the highest micron rating. They start out at about 40 microns   and go down to 20 microns over time. “A sand filter starts to clean better   the dirtier it gets,” says John Ott, Western Regional Technical Training   Manager at Hayward Pool Products, Elizabeth,   N.J.

Because   of this high micron rating, the water in a sand-filtered pool could start to   look cloudy. When this happens, simply add a good clarifier. A clarifier will   gather all of the small pieces of debris that pass through the filter and   clump them together into a larger piece of debris that will become trapped in   the sand filter’s crevices.

Backwashing   a sand filter

The   only way to clean a sand filter is by backwashing it. And it’s important to   remember that this is a two-step process.

First,   backwash the filter for at least two minutes, or until the water runs clear.   In normal run position, the sand gets packed down. During backwashing, the   sand rises and separates, thus releasing the debris trapped inside and   allowing it to flow out of the filter.

Second,   allow the filter to sit for 15 to 30 seconds. This lets the sand inside   settle down again. Then, set the backwash valve to the rinse setting and   rinse the filter for 30 seconds, or until the water runs clear.

A   common complaint about sand filters is that a small amount of dirt will shoot   back into the pool after backwashing. This is often because the second   backwashing step — allowing the filter to sit for 15 to 30 seconds so the   sand can settle and re-trap the dirt, followed by rinsing the filter — was   not performed. Bypassing this step may cause some dirt to escape the filter   and re-enter the pool. With proper backwashing and rinsing, and the addition   of a clarifier, a sand-filtered pool should stay clean and blue.

Cartridge   filters

Developed   in the 1950s, cartridge types are the newest of the swimming pool filters.   They are also the simplest to maintain, which is why they are so popular   today.

The   cartridge of the filter closely resembles a car’s air filter, but much   taller. The cartridge material is made from a pleated polyester cloth. As   water passes through the pleated material, dirt particles and debris are   trapped within the pleats. A new cartridge filter can strain out particles at   about 20 microns, but will go down to as low as 5 microns. The micron rating   actually gets lower as the filter gets dirtier.

The   cartridge must be removed for cleaning, as the filter cannot be backwashed.   It’s a good idea to clean a filter every six months to a year, depending on   the bather load and the size of the cartridges. (See “The Pressure’s On” for   more information on when to clean a filter.)

To   clean the filter, remove the cartridge and simply hose it off.

After   hosing the filter clean, take a minute to inspect it. The pleats should be   straight, not buckled or crooked. Also, inspect the molding on the top and   bottom of the cartridge. Is it in good shape, or is it starting to tear away   from the pleats? Buckling and tearing are signs that the cartridge is getting   old and needs to be replaced.