Filter out your pool problems – cleaning swimming pools

Michael Walsh

There’s a lot to think about in maintaining a pool. The water has to look clean, which means the pool itself has to be clean. The water also has to feel clean; this calls for the operational triangle; circulation, filtration and chemical treatment.

Cleaning the Pool

The first step to getting members to use your pool is making it clean and attractive. A clean, properly cared for pool is an asset; lack of proper maintenance can turn it into a nightmare. There are different types of pool cleaners, including self-propelled, automatic units and affordable, portable vacuum pumps, any of which will help clean the walls and bottom of the pool.

None of these units should be used when people are swimming, and, as with any electrical device used around water, they must be connected to an electrical outlet protected with a ground fault interrupter. This will lessen the risk of potentially fatal electrical shocks. in fact, all electrical wiring and devices around a swimming pool are subject to the very stringent requirements and standards of the National Electrical Code. You need to be aware of these standards, particularly as they have been updated several times in the past few years, and the proper protective devices may not have been included in older clubs.

Regardless of the particular piece of equipment you use, daily attention, such as vacuuming, brushing and deck cleaning, will provide the clean, pleasing environment your members expect. A variety of specialty cleaning compounds are available to help in cleaning not only the pool walls, but also the equipment around it; diving boards, gutters, ladders, walkways and decks. While stains, scale and surface deposits are not particularly harmful to the user, they are not attractive and reflect poorly on club-housekeeping practices. You may not need an expensive product to do these jobs. A small amount of soda ash (sodium carbonate, an alkaline material used to raise and control pH) will do wonders in cleaning the scum line or oil line off the sides of the pool.

The Operation

Cleaning the water in the pool is a little more complicated than cleaning the pool. To provide clean water, you must understand the operational triangle of proper pool maintenance. This triangle consists of three separate operations: circulation, filtration and chemical treatment. Each of these systems must be operating and maintained correctly. If any one is out of balance, you will not have a clean, usable pool.


Swimming pool water is continuously circulated from the pool to the filter system and chemical-treatment system and then returned to the pool. Unless your system is specifically designed to allow shutdown periods, the circulating pump that moves the water should run around the clock.

Understanding pool operations means knowing the recirculation or turnover rate for your pool. A six-hour turnover of water in a pool is standard in the United States. This means the entire volume of water from the pool should pass through the filtration and treatment systems once every six hours. To determine the recirculation or flow rate for your pool, calculate the cubic feet of water and multiply that number of 7.5 to get pool gallonage (i.e., length times width times average depth times 7.5). Divide this number by 360 to determine your minimum flow rate in gallons per minute, then check your recirculating rate. Read the pool system flow meter to determine your actual flow rate. Cloudy water can often be the result of heavy usage and too little turnover.

The dirtiest, most contaminated water in a swimming pool is the top two or three inches. A properly designed swimming pool recirculation system must skim the top of the water via a continuous overflow lip around the entire edge of the pool. This skimming process ensures that the surface dirt and debris are continually being removed. One of the biggest errors made by pool operators is failure to maintain proper water levels in the swimming pool. When the pool water level is below the overflow lip of the gutter or skimmer, surface debris is not being removed.

You can control water level by a variety of means, including automatic water-level control equipment. If an automatic system is not available, the pool operator must keep a close eye on water levels, particularly at the end of the day to ensure that the pool is properly skimming during the night

The recirculating pump receives water from the perimeter overflow gutter and the main drain of the swimming pool. Incorrect water level or restrictions in the lines prevent proper circulation. Closing the wrong valve or forgetting to clean the hair and lint strainer (located at the front of the pump) on a daily basis can ruin a pump in a matter of hours.

Some facilities have a chemical treatment system that injects pool chemicals on the suction side of the recirculating pump. Occasionally, gas chlorination systems utilize the differential pressure from the discharge or pressure side to the suction side of the pump to inject a gas chlorine solution. These practices only benefit companies that sell pumps. Check your chemical injection points, and, if you are adding materials at the suction side of your pump, take whatever steps are necessary to properly add chemicals downstream of the filter immediately prior to the water returning to the pool. Your pump and filter will last much longer this way.

To properly understand and monitor the operation of your circulating system requires that you have a flow meter that measures flow in gallons per minute. This meter or measuring device is installed in the pool piping and should be checked regularly. Gauges are also necessary on the recirculating pump and filter system. A pressure gauge should be installed on pump discharge and a vacuum gauge on the pump suction. Using the pressure and vacuum readings can allow you to read the pump curve (furnished by the manufacturer) and determine your actual flow rate.


Clean water means continually filtered water. The water in your pool is passed through the filter by the circulation system to remove “turbidity.” Turbidity is the organic and inorganic material suspended in pool water. One of the questions every pool owner asks is, “What is the best filter?” There is no such thing as the “best filter.” Each has its own unique characteristics and each is appropriate for certain installations. You could filter swimming pools with cheese cloth if you had enough of it. To properly select and understand swimming pool filtration, you have to understand how different types of filters operate and what your needs are. If properly sized, any filter will provide clean, clear water.

Three different types of filters are commonly used in today’s pools–sand, diatomaceous earth and cartridge. Additionally, each filter is available as a pressure- or vacuum-operating configuration. In pressure filtration, the water from the swimming pool is pushed by the recirculating pump through a closed tank. In vacuum filtration, pool water flows into an open top filter tank and is pulled out by the recirculating pump. The swimming-pool filtration system is selected and sized according to recirculation or turnover rate–once every six hours being the norm.

The advent of whirlpools or spas has required an entirely new look at filter sizing. Rather than basing filtration sizing totally on pool volume, the number of people actually using the pool is now also being taken into account. A 50,000-gallon diving pool may actually have a much lower filtration requirement than a 1,000-gallon whirlpool. Smaller, high-use pools in public facilities are now being designed for turnover rates of every 30 minutes, while whirlpools and hydrotherapy tubs completely exchange the water every two to three minutes.

Filter sizing is based not only on turn-over rates, but also on gallons per minute, per square foot of filter area. Each filter has a particular rate at which it performs most efficiently. Operating above or below the recommended flow rate will usually result in unsatisfactory water conditions.

Sand filters, which have been around for a number of years, are prevalent today There are two types of sand filters: the conventional or rapid-flow sand filter and the high-rate filter. The rapid-flow sand filter operates at approximately 3.0 to 7.5 gallons per minute, per square foot, while the high-rate filter is often operated at up to 20 gallons per minute, per square foot. Sand filtration cleans the water by passing it through a bed of sand, where the small interstices, or openings between the particles of sand, trap the dirt and debris. In time, an abundance of matter accumulates in these pores, and the flow of water must be reversed to expand the sand bed and flush out the debris.

Effective filters go hand-in-hand with proper water chemistry. Otherwise, calcium and other mineral deposits can clog or encrust these interstices, turning your sand filter into a large hunk of concrete. When this calcification occurs, the filter bed will channel, allowing the water to bypass without being filtered. There is a large variety of compounds that can prevent this problem from occurring. You can add these cleaning materials into the filter, to dissolve and remove the scale and calcium deposits and reopen the filter. Yearly inspection of the sand is necessary to recognize and prevent this problem and others.

You judge when you need to backwash a sand filter by watching your pressure gauges. A high-rate sand filter must have operating influent and effluent pressure gauges. The influent gauge reads the pressure on the incoming side of the filter and the effluent gauge reads the discharge pressure. Most manufacturers suggest that it is time to backwash the filter when you reach a 10-pound differential between the readings on the influent and effluent pressure gauges. Backwashing is accomplished by reversing the flow that expands the sand bed and flushes out the dirt and debris.

Gauges are relatively inexpensive and should be replaced at the first sign of malfunction. Without properly operating gauges on your filter system, it is impossible to correctly operate your filter.

The majority of sand filters in community pool filter systems are pressure filters. many newer systems, however, will utilize vacuum sand filtration, where the sand is contained in an open-top tank, to which a pump is connected. Both filters operate in virtually the same way and will provide outstanding water quality with proper operation and maintenance.

Another type of filtration system you will encounter is the vacuum or pressure DE (diatomaceous earth) filter. This filter consists of a round or square framework tightly covered with a fabric material, usually a polypropylene cloth. This filter element has one or two connections to a filter manifold, which then conveys to the pump. The element is coated with a thin layer of diatomaceous earth (the skeletal remains of very small marine animals). Each of these particles has numerous tiny holes. The suspended dirt and debris are removed as the water is pushed through these pores or holes. In time, these small pores become plugged with the suspended particles removed from the water as it is pushed or pulled through the element. The DE coating must then be flushed off and replaced with a new coat.

As in sand filtration, filter operation is monitored via vacuum or pressure gauges. On a vacuum DE filter, the diatomaceous earth coating is replaced when the vacuum gauge reading is approximately 12-15 inch mercury. In pressure DE filtration, the filter is cleaned and recharged after approximately a 10-pound increase in the influent pressure.

Proper operation of a DE filter means maintaining the condition of the filter element. If operated without a coating of diatomaceous earth, the filter covering will become permeated with dirt. The resulting reduction in porosity will cause very short filter runs. Diatomaceous earth filters are also sensitive to power interruptions. If you have a power failure or outage and the filter pump is off even for a few moments, the DE coating can break away or fall off the element. The filter will then need to be cleaned and recharged.

Diatomaceous-earth filter elements will also accumulate rust and iron deposits, calcium, and lime scale. The element can be cleaned with the same specialty chemicals used to clean sand filters. These materials will break down the deposits and restore proper filtration. In the event a DE filter is not properly maintained, the fabric covering may be stretched or even tom, releasing small amounts of diatomaceous earth into the pool water. This will cause cloudiness and eye irritation. Filter elements and their coverings must be cleaned of iron and scale regularly and may need to be replaced every two to five years, depending upon the care and maintenance they receive.

To properly operate your DE filter you need to understand what the pre-coat requirements for your filter are. The pre-coat requirement is the amount of diatomaceous earth required to coat-out the filter elements. Every filter manufacturer recommends different amounts of diatomaceous earth to be used in this process, but a normal rule of thumb is approximately one pound per 10 square feet of filter area. Many vacuum DE filters may utilize a body-feed system. Body feed means continually introducing a very small amount of diatomaceous earth through a slurry pump or volumetric feeder directly into the feeder at all times. This helps to maintain an even layer of diatomaceous earth on the filter element. If the flow rate in your filter is maintained within normally accepted ranges, approximately one and one-half gallons per minute per square foot of filter area, a body feed is really not required.

One good trick to use in operating a DE filter, be it vacuum or pressure, is to sprinkle a coffee can or two full of DE slowly into the gutters or skimmers around the pool every morning. The water washing into the gutter will then take this small amount of DE, mix it thoroughly, and deposit it back on the element. Make sure loose DE doesn’t wash into the pool. This practice will extend your filter run and help maintain an even coating on the filter.

A third type of filter very common in club pool operations is the cartridge filter. A cartridge filter consists of an artificial filter medium, usually consisting of a stiff nylon and polypropylene material that is corrugated and formed into a cylinder with the ends scaled. This cylinder has a center drain channel, and the water is pushed through the material and out through this center drain. A cartridge filter will consist of one or more individual cartridges, which are cleaned by removing them from the filter system and hosing off the dirt and debris. Pressure cartridge filters, the most common, should be cleaned after a 10-pound rise on the influent pressure gauge.

Any type of filter system is susceptible to oil fouling, especially cartridge filters. Body oils, greases, and tanning products can coat-out in the filter media and cause very short filter runs. Using acid to remove these oils causes the oil to become set and makes it very difficult to remove. The same products that are used to clean other types of filters, work well to remove all deposits. A solution of trisodium phosphate also breaks down these greases and oils and will restore the cartridge to its original condition.

One good practice in using any type of cartridge filter that is opened for cleaning is to mark the location of the lid gasket so that the gasket is always reinstalled in exactly the same orientation. This will make it much easier to re-seal the tank. Additionally, a light coating of petroleum jelly on wing nuts, operating handles and levers will make it much easier to remove or operate this equipment. A special waterproof lubricating compound is available from pool stores.

Chemical Treatment

The third leg of the operational triangle is chemical treatment. The maintenance of proper water chemistry is probably the most important, most talked about and least understood area of pool management. If you understand nothing else, make sure you understand water chemistry. Chemical manufacturers and suppliers spend thousands of dollars each year to convince you that their product is superior to all others. They will go to great lengths to help you understand pool water chemistry and provide excellent literature. Read it, be aware of it, evaluate it, and see how it applies to your particular installation.

Chemical water treatment, in brief, consists of adding some form of disinfecting agent, usually a chlorine product, to kill bacteria and algae in the pool water. Algae grows only in the presence of sunlight. Thus, it is usually not found in an indoor pool. Regardless of the type of chlorine product used, a solution of hypochlorous acid created in the pool water actually does the disinfecting. The levels of hypochlorous acid are measured using a standard pool-test kit, and, if maintained at proper levels, will produce bacteriologically safe pool conditions.

Bromine systems, either in stick or tablet form, produce a similar compound, called hypobromous acid, which does the disinfecting. Bromine compounds are stable in hot water and are often used in spas, whirlpools, and hydrotherapy installations. Several new disinfection systems have become available in the past few years. These include ozone and ultra-violet systems. Ozone-generating systems are becoming very popular and provide an excellent supplement to the basic disinfecting system. None of the new systems produce a residual of disinfectant in the water. Thus, they cannot be used alone.

There are four main types of feeders for disinfecting compounds: gas chlorinators, solution metering pumps, volumetric feeders and erosion feeders. The best advice regarding gas chlorinators is, if you have one, understand how to use it; if you don’t leave it alone. Your chlorine gas supplier will be happy to provide specific instructions and training on how to safely use chlorine gas. Chlorine gas, like many other pool chemicals, is quite dangerous and potentially damaging to your equipment.

The second type of chemical feeding system mentioned is the solution metering pump. These positive displacement pumps must be cleaned on a regular basis, as the solutions which are being delivered tend to coat-out or precipitate on the internal components, causing these components to stick and the pump to lose prime.

Those units pumping calcium hypochlorite solutions, bleach, or soda ash tend to clog particularly quickly. One way to prevent this clogging is to regularly remove the foot valve (the small device at the end of the suction hose) and drop it into a bucket of clear water for two or three minutes. Then place it into a diluted solution of muriatic acid. As this solution enters the metering pump, it will dissolve the deposits and normally return the pump to proper operating condition. After it has pumped muriatic acid for a few minutes, take the foot valve out and again place it into clean water. Let it pump clear water for at least five minutes so that you purge all the muriatic acid from the line and place it back into your chemical crock.

The third type of feeder you will encounter is the volumetric feeder. This consists of a large hopper that has a worm gear at the bottom. Through the movement of this worm gear, very small, precise amounts of chemicals are continually introduced into the pool water. This piece of equipment is normally encountered only in very large commercial water treatment or swimming pool facilities and will usually not be found in smaller pools.

One of the more common types of disinfecting equipment is an erosion feeder. Most often used with bromine compounds, this filter is a small sealed vessel through which water flows. The flow of water over and around sticks or tablets of compressed sanitizer dissolves and returns disinfectant to the pool. A small control valve on one side of the feeder can restrict the water flow and vary the amount of chemical being introduced to the pool water. After refilling an erosion feeder, it is a good idea to fully open the flow valve and leave it open for 15 to 30 seconds. This helps to purge the feeder of chemical deposits. It is also good practice to remove all material from the feeder once every month or so and completely hose it out, flush it clean and place it back in operation.

In addition to sanitizing or disinfecting compounds, a variety of chemicals will be used to adjust and maintain the swimming pool pH. The products used to sanitize pool water will be either alkaline or acid. As they are added to pool water, they will cause the pH to change (pH is a scale of 0 to 14 measuring the acidity or alkalinity of the solution). It is critical that swimming pool water be maintained at a pH between 7.4 and 7.6

Depending upon the pool disinfecting chemical used, small amounts of soda ash (sodium carbonate) or muriatic acid will keep the pH in the proper range. Additionally, other chemicals added to the pool from time to time balance the hardness or alkalinity of the pool water. Most swimming pool chemical distributors have elaborate water-testing equipment, and they can advise you as to the amounts and kinds of chemicals necessary to properly maintain your pool facility.

Be very careful when using any type of swimming pool chemical. While relatively safe if handled with care and respect, these chemicals can burn or injure the inexperienced or careless user. Never mix two chemicals. The reaction between a chlorine product and muriatic acid is extremely violent and rapid. Mixing together two products in a solution crock can cause the contents to explode in your face. Solution crocks should be clearly marked in terms of acid, soda ash, or chlorine and are best placed on opposite sides of the room. Treat all swimming pool chemicals with respect and have your chemical supplier explain their individual characteristics and use.

There are other pieces of pool equipment that must be cleaned and maintained on a regular basis. For instance, hair and lint strainers must be cleaned daily. If not, they will clog and restrict the flow of water to the pump, which means you won’t be pumping water but that you will be buying either new impellers or a whole new pump. Common practice is to have two strainer baskets so that when you take one out you can let it dry before cleaning. Don’t try to clean it wet. When it is dry, a wire brush will easily remove the material from the strainer.

If you find that the side of your strainer basket is beginning to bow out toward the pump, this is an indication that you are not cleaning it often enough and are putting a restriction on the pump. Never operate the pump without the strainer basket in place, as you can quickly clog or ruin a pump impeller.

It is also critical to control the dust in the mechanical room. If you are using diatomaceous earth, soda ash, or other granular chemical products, there will be a very fine dust present. This fine dust can be pulled into an air cooled motor and quickly cause damage. Try to control the dust and the storage of granular material, as it can also irritate eyes and the respiratory system. It will also benefit the operation of your pump and motor to establish good air circulation in the mechanical room. Do not block air vents and make sure that exhaust fans are operative. If you do not have adequate air flow throughout the mechanical room to exhaust the heat produced by various pool equipment, you may find your motor controls tripping out on a regular basis.

Other pieces of equipment needing routine care are the system valves. Valves, whether they be butterfly, gate, ball, or wafer valves, are the controlling mechanisms in any swimming pool system. There are common procedures to follow, such as never closing a valve quickly. Turn it slowly, because if you close a valve too rapidly, you will create a water hammer or a high-pressure surge through the system. The banging or knocking in your home plumbing when a faucet is closed quickly is the same phenomenon that occurs in a pool mechanical system. The high flow rates in a pool system, however, can actually break piping because of the forces transmitted by closing the valve too quickly. You should never force a valve.

If you meet an obstruction and firm pressure will not allow the valve to seal, don’t use a 36-inch pipe wrench on the handle to try to close it; it means there is something wrong in the valve. If you are a mechanical wizard, tear into it. If not, get your service company or maintenance personnel to remove the valve and find out what is wrong. It is very common to fined a small rock or piece of debris in the valve. If you force it, you will destroy the sealing mechanisms in the valve and end up having to replace the entire valve mechanism.

It is a good idea every few years to actually demount valves, grease and lubricate external components and check to make sure than they are in good operating condition. It is not uncommon to see large amounts of water being wasted because of a leaky valve on a backwash line.

Water Heaters

Another sensitive area in pool operation is the water heater. The key to operating the pool water heater is maintaining proper water chemistry balance. pH values much to either side of the desired range of 7.4-7.6 mean that you will be buying new heat exchangers or replacing heaters on a regular basis. Make sure that you have balanced and continued flow through the heater at all times. Electric heaters are susceptible to element burnout if the flow of water is interrupted for only a few seconds. Many electrical heaters use separate flow switches to interrupt heater operation immediately in the event the pool circulating pump is turned off or a valve inadvertently closed. Your heater manufacturer or equipment supplier can help you in sizing and balancing the flow so that you get the proper heat or temperature rise from the heater.

If you have a gas pool heater for your indoor or outdoor pool, make sure that you are providing adequate combustion air to the pool heater. This means that the vents or louvers in the pool equipment room are kept open. If you are using a gas pool heater in the winter and it gets cold in the mechanical room, do not attempt to restrict the flow of air in through the louvers.

Be sure to keep water out of your underwater lights. Clean them on a regular basis and use a small amount of lubrication on the lens gasket to maintain a proper seal. if you have water present in any of your lights, turn them off Determine the cause for water leakage and clean and dry the fixture before it is turned on.

All new swimming pool electrical systems are protected by a ground fault interrupter. The possibility for electrocution is always present in a system which is not GFI protected. If you have an older pool facility, your electrical system should be checked by a licensed electrician and proper GFI protection installed. Also remember that underwater lights may not be rewired. The light socket is encapsulated in a special potting compound installed at the factory. If something happens to the fixture, you have to replace the entire light. If you try to re-wire it yourself, install new sockets or replace the cords, or you expose your patrons to a great risk of injury from electrical shock.

A pool operator should also keep a close eye on the railings, fittings, ladders and steps. Check the bolts, check the fittings and make sure that fittings are tight. Bolts on pool ladders and dividing stands will deteriorate over time and might break when stepped on. Make sure that handrails are securely fastened and don’t wobble.

Lifesaving safety and rescue equipment are necessary and required by most state codes. As the operator of a swimming pool facility, it is your responsibility to make sure that the proper equipment is present and functional. Your staff must be aware of this equipment and be trained in its proper use. While this equipment is used infrequently, it is needed in life-threatening situations.

The overall operation of a swimming pool facility often appears to be a complex, time-consuming task. This perception, however, is often the result of a housekeeping or maintenance which has been neglected. Properly operating a pool means careful daily attention to the many little aspects that help provide an enjoyable, pleasurable swimming pool environment Keep your pool and its mechanical systems clean, attractive and properly maintained. Make swimming a pleasurable, enjoyable experience for your guests. Your efforts will be repaid many times over in increased revenue, patron satisfaction and facility use.

COPYRIGHT 1993 National Recreation and Park Association

COPYRIGHT 2004 Gale Group

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