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Understanding Pool Filtration & Filter Media

Pool water filtration is one of the most important aspects of a swimming pool. For obvious reasons, it is imperative that the water be clean and clear. Swimmers and lifeguards require this crystal clear water for several reasons, whether it be for swimming laps, knowing when to start a flip turn, or being able to see all of the pool patrons clearly in order to effectively monitor the pool. Furthermore, the water needs to be clean and free of bacteria so that swimmers do not leave with an illness. While there are many systems that work in conjunction with a pool filter to help keep the water healthy, the physical pool filter, which is available in varying styles and options,  is the focal point in providing clean, clear water. 

 

In most cases, pool water is pushed by the filtration pump through the filter system. Other systems operate using the pump on the other end of the system where it can pull the pool water through the filtering system. Either way, what happens is essentially the same – as water passes through the filter media, physical dirt and bacteria are removed, and clean water continues from the filter through the remainder of the recirculation system for further treatment, and returned to the pool. 

 

The style of filter, along with the media being used, will determine the effectivness of the filtration system, as differing types of filter media actually filter different sizes of particles out of the water.

 

#20 SILICA SAND

The reason that pool filters use #20 silica sand (also known as 20 grit or 20 grain, 0.45-0.55 mm sized granules) is that it is small enough to filter out micro bacteria, yet large enough that it doesn’t get pushed through the whole plumbing system and cause other problems. In addition, larger granules are unable to filter the small bits of dirt and bacteria that it is intended to. #20 silica sand can filter out particles down to 20-40 microns in size. As water passes through the sand (which is essentially a really small stone, which is jagged on all edges if looked at through a microscope), the jagged edges catch tiny dirt and bacteria particles, eliminating them from the pool environment.

 

Depending on various factors (bather load, bather cleanliness, etc.) sand filters need to be backwashed every so often to clean the sand. If the sand filter is not maintained, it will stop filtering as it is supposed to. Backwashing is completed by running water through the system backwards to release all of the dirt and bacteria that has been caught by the sand, and must then be removed from the filter tank.  When the water being discharged is clear, you are finished backwashing. Most filters have a sight glass so operators can physically see the dirty water at the beginning of backwashing eventually turn clear when the process is done.

 

Sand is the oldest and most commonly used filtration media, because it is effective and one of the most cost friendly options. However, after many cycles of filtering and backwashing, the granules become rounded, eliminating their filtering capabilities. The sand should be changed approximately every 5 years, depending on usage and backwashing frequency. 

 

ZEOLITE

Zeolite is an all-natural product that is gaining popularity in the pool industry. It is about half as dense as #20 sand, meaning you can use about half as much as what is recommended for the filter. For example, if your filter requires 100 lbs. of sand, you would only require about 50 lbs. of zeolite. This type of filtration media is a bit more expensive than sand, so there will be a higher upfront cost. With the ability to filter particles down to 5 microns, Zeolite is comparable to a D.E. filter, and better than sand, though D.E. filtration systems are much more expensive than a sand filter system charged with a zeolite media. Zeolite lasts about the same amount of time as sand with regular use, which is approximately 5 years. 

 

CRUSHED GLASS

Crushed glass is a new addition to the filter media family. Made from recycled glass (good for the environment) that is crushed to the same size as #20 sand, it filters using the same principles as sand. In comparision to sand, crush glass lasts longer (approximately 10 years) and can help in removing micro particles with its negative charge. When using crushed glass, more of the filter media is used for filtering because it utilizes more of the filter tank, as opposed to sand which typically only uses the top four to six inches. This means there is a shorter backwash time, saving more precious water. 

 

DIATOMACEOUS EARTH (D.E.)

Diatomaceous Earth (D.E.) filters the water very effectively, down to two to six microns, however they are more expensive systems and take up a larger footprint in the mechanical room. D.E. is tiny fossilized skeletons of sea plankton that are coated onto a grid of filter elements that sit in a tank where the pool water passes through. The water can either be pushed or pulled through this system.  D.E. is considered carcinogenic, and proper handling and storage techniques, including protective gear and breathing protection, must be adhered to. D.E. filters are able to be backwashed for cleaning, but the media is lost in the process, and needs to be periodically replaced. D.E. systems do not eliminate chloramines which cause the chlorine smell commonly noticed at an indoor pool, so using a UV system is strongly recommended in order to eliminate them (a reccommendation for all pool filters). 

 

REGENERATIVE FILTERS

Regenerative filters are another new option in the pool market. They also utilize D.E. or a synthetic substitute, however are a bit more complex in their design. In a traditional D.E. filter, only the channels and depressions of the surface of the filter media trap particles. The underside of the D.E., the side attached to the grid, has a reduced ability to filter. In a regenerative filter, the media is held on multiple tubes, or “fingers”, that are periodically “bumped”, causing the filter media to fall to the bottom of the tank. The filter media is then redistributed, allowing unused sides of the media to be used for filtration as well. Regenerative filters offer a large amount of surface area with a relatively small footprint and are often toted for their water saving qualities due to the reduced need for backwashing and D.E. replacement. The water savings may or may not offset the cost of these units, therefore your individual return on investment should be evaluated before purchase.

 

Thanks to several innovations and advancements in technology, there are many options available when considering pool filters, and filtration media. It is important to consider all of the factors specific to your project when choosing a filtration system, or to at least understand what you want and don’t want when planning with the pool designer that is working on your project. You want to have the right filtration system and media for the facility to ensure it is operating in the most economical way.

 

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Salt Water Chlorination: Is it the Right Option for your Facility?

Salt or no salt? That is the question! Or at least one of the most common questions being asked by pool owners and operators these days. Every pool owner has their own set of reasons for wanting salt or not wanting salt. There are many questions regarding the mechanical equipment at the facility, finishes of the pool, uses of the pool, local bylaws, (just to name a few) that must be answered before jumping to any decisions. Additionally, the owner must be aware of the many myths regarding salt water systems and chlorine systems alike before making any decisions. They must also understand that a salt water pool doesn’t mean you will be swimming in ocean water! Windows to the Universe team states that salt water pools typically have 3,000 to 6,000 ppm, while the ocean is about 35,000 ppm.

 

MECHANICAL EQUIPMENT

When changing a liquid chlorine sanitized pool over to a salt water system, or when building a pool destined to be salt water, the mechanical systems must be selected properly.  Everything from the pumps, filters and heaters must be designed and approved for use in a salt water pool.  If this is not done, manufacturers will not honour warranties, and there will be damaged equipment much prior to their normal lifetime.

 

POOL FINISHES

The finishes of the pool need to be considered when contemplating a salt water pool as certain finishes do not last as long under salt water conditions.  Liners, tile and plaster finishes all have their own issues when it comes to salt, so owners must investigate each option thoroughly and ensure whichever option is chosen is installed properly. As with any sanitation system, monitoring and proper balancing is also very crucial in the lifetime of the finishes. 

 

Fixtures such as hand rails, underwater lighting fixtures, and rope anchors need to be properly chosen when going with a salt water pool as they will corrode faster without being constructed of proper materials and properly maintained. The image above shows a hand rail in a salt water pool that is rusting due to the salt. Think of what salt use on our roads does to our vehicles and infrastructure during the winter months.  The same type of damage will happen to a pool that doesn’t have all of its components designed for salt water use.

 

POOL USE

Primary uses of the pool under consideration for salt water should also be considered.  A pool that is primarily for lap and competition swimming where there is high swimmer volume and high exertion may want to shy away from a salt system, as it will require much more monitoring of the chlorine levels to ensure they are in accepted ranges.  Yes I said chlorine.  Salt water pools still have chlorine in them.  They use a chlorine generator system involving a process called electrolysis to produce its own chlorine, rather than adding liquid chlorine directly to the water.  A therapy pool with low patron turnover may be a better candidate for salt water, as it will be easier to keep the pool balanced and may increase user comfort.

 

LOCAL BYLAWS

Local bylaws are another very important item to look into when considering salt water in your pool.  Especially for commercial pools, salt is typically not permitted to be the primary source of sanitation.  Most municipalities still require salt water pools to have a secondary sanitation system installed, typically liquid or tablet chlorination.  Furthermore, when draining the pool, salt (and chlorine) levels usually must be brought down to low levels in order to legally be dumped into the municipal sewage treatment system.  Always check local bylaws for your stipulations prior to draining your pool.

 

Pool owners need to ensure that they do as much homework on salt water chlorination as necessary to ensure that they have made an informed decision.  There are too many cases of owners not taking all of the necessary steps required to properly operate a salt water pool, and have a seemingly endless repair bill. As with any large expenditure, always ensure you are working with qualified pool designers and builders when constructing a new pool or doing a renovation, no matter what sanitation system you are going with. 

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