POOL BASICS

Swimming pools come in many different shapes and sizes, but nearly all of them, from the backyard personal pool to the water park wave pool, work in the same basic way. The concept behind these is the use of a combination of filtration and chemical treatment to continually clean a large volume of water.

A typical swimming pool needs seven major components:

• A basin / pool shell
• A motorized pool pump
• A water filter (normally sand filter)
• A chemical feeder (manual or automatic chemical dosing system)
• Drains / Skimmers / Overflow gutter
• Return inlets
• PVC plastic plumbing (pipes and fittings) connecting all of these elements

Types of Pools

The main difference between different types of pools is how the basin or pool shell is constructed. There are several different pool styles, each with their own advantages and disadvantages:

Above-ground pools are the cheapest construction option, as well as the easiest to build. Most above-ground pools are made from prefabricated kits: there is a great variety of these available, from ones which are very simple to install to more complex larger ones which need to be installed by expert pool builders. Firstly, the ground needs to be levelled to form a flat building surface. Then a perimeter track is assembled - this supports the outer wall (which can be made of metal, plastic or wood). Next, the filtration system is installed – the type of system varies in accordance with the different models of above-ground pools. Advantages of this type of pool are that they are relatively inexpensive and not permanent – it is relatively easy to disassemble the pool and move it to a new location, which can make it an ideal solution for people who are renting property or do not want a permanent fixture in their house. For more information on above-ground pools, contact us at info@a-technologies.com.

Fibreglass pools are made from fibreglass-reinforced plastic that has been moulded into a basin shape. To install the pool, a construction crew digs an appropriately sized hole, lays the necessary plumbing and lowers the preformed pool structure into the hole. The pool is then levelled, the piping connected and the space around the pool shell is backfilled with sand. In many cases, the pool is surrounded by a concrete deck structure for additional support.

Vinyl-lined in-ground pools are structurally similar to above-ground pools. The construction crew digs a hole and assembles a metal, plastic or wood frame wall around the hole's perimeter. Sand is then laid along the bottom of the hole and the vinyl lining is fixed to the structural wall. These pools are less expensive than other in-ground designs, but not as durable. Typically, the vinyl liner needs to be replaced every 10 years or so.

Gunite pools are the most popular type of pools in places such as South Africa, Australia and the United States. To build one of these pools, the construction crew digs a hole, puts the plumbing in place and assembles a framework grid with 3/8-inch steel reinforcing rods (rebar). The rebar rods are spaced about 10 inches apart, and secured together with wire. When the grid is in place, the crew sprays a heavy coating of gunite, a mixture of cement and sand, around the rebar. The sprayer unit combines dry gunite mix with water just before spraying -- this produces the wet concrete material. The crew trowels the gunite smooth and lets it sit for a week or so before applying a smooth finish to the rough surface. The most popular finish for this type of pool is called marble plaster (actually a mixture of cement and marble sand), but a lot of people finish their pools with special concrete paint. Gunite pools can also have tile, exposed aggregate or even fiberglass finishes. Gunite pools (and their cousins, shotcrete pools) are highly durable, and they can be built in any shape or size.

Poured-concrete pools are similar to gunite pools, but they are more difficult to build. Instead of spraying concrete material around a rebar framework, concrete is actually poured into conventional wooden forms. In masonry block pools, the walls are constructed with concrete blocks. Stainless-steel pools (Myrtha System)

Pool Trivia: Did you know?

Pool Filtration Systems

As we saw previously, the water in a swimming pool needs to circulate through a filtration system to remove dirt and debris. During normal operation, water flows to the filtration system through the main drains at the bottom of the pool and the skimmers around the top of the pool.

The main drains are usually located on the lowest point in the pool, so the entire pool surface slants toward them. Most of the dirt and debris that sinks exits the pool through these drains. To prevent people’s hair or limbs caught in the plumbing, it is recommended that two or more drains are installed to reduce the suction pressure. Antivortex drains and covers, which divert the flow of water to prevent a dangerous vortex from forming, can also be used.

In the system described above, the floating skimmer flap, where the water enters the skimmer, swings in and out to let a very small volume of water in at a time. To catch debris effectively, the goal is to skim just the surface level. The water flows through the skimmer basket, which catches any larger debris such as twigs and leaves, and needs to be cleaned regularly to prevent clogging of the suction line. In addition to the main inlet, the skimmer system can have an optional secondary equalizer line leading to a drain below the surface level. This line keeps the skimmer from drawing air into the pump system if the water level drops below the level of the main inlet.

Overflow Pools

Not all in-ground pools have skimmers. How then is the water drained from the pool and re-circulated? Pools that do not have skimmers normally have what is called an overflow system. A channel is constructed around the edge of the pool and inside this channel there are drains (normally called gutter drains) which collect the water and convey it to a balancing tank (surge tank). This is a collecting vessel, which can be made of fibreglass, plastic or concrete depending on the size and nature of the application, and which is used to “balance” and compensate for the water leaving the pool through the drains (which is not always flowing at a constant rate as it is in a skimmer pool). This balancing tank should have a water-level regulator connected to a water-supply line. With this system, when the water reaches a predetermined low level, a valve will be activated which allows water from the supply line to fill the tank. This is to ensure that there is always sufficient water for the pump to operate correctly without sucking air. The water is pumped through the filtration system and back out through the return inlets (wall inlets) around the side of the pool. This system involves a lot of suction, but if the pool is built and operated correctly, there is virtually no risk of suction holding somebody against one of the drains. The only way the plumbing system could exert this sort of suction is if there were only one open drain. As already mentioned above, in a safe pool, there are always multiple main drains as well as several skimmer drains, so if somebody or something blocks one drain, the pumping system will pull water from one of the other drains. This eliminates the suction on the blocked drain. Many swimming pools also have one or two vacuum points, which are only used in pool cleaning. Normally, these vacuum points are connected to the main filtration line although they may have their own separate pumping system. Automatic pool cleaners or other cleaning equipment can be attached to these vacuum points by means of vacuum hoses – these use the suction created by the pump to suck water (together with any dirt or sand in the pool) in much the same way as an ordinary vacuum cleaner works (with air).

Swimming Pool Pump Systems

The heart of the pool system is the water pump. In a typical pump system, an electric motor spins an impeller inside the pump housing. The impeller creates a suction, drawing water from the drains, vacuum points, skimmers or gutter drains and then pushing it through the filter and back out to the return inlets. The pump has a strainer basket which catches leaves and other large debris that could clog the internal mechanisms of the pump. Pumps are usually made of different varieties of plastics, metals, cast iron and even bronze, and they have different pumping capacities (measured in either kW or hp), which are calculated in accordance with the volume of pool water and the turnaround time (i.e. the time it takes for all the water in the pool to be recirculated through the filtration system). This calculation will depend on factors such as weather conditions (temperature in particular) and bather load (i.e. number of people that will use the pool).

Pool Filters

The filters in this system are high-rate sand filters. Sand filters consist of a large tank, which is usually made of a polyester/fibreglass mix but can also be made of polyethylene, stainless steel or other materials depending on the application. During filtering operation, dirty water from the pool comes in through the filter's inlet pipe, which leads to the water distribution head inside the tank. As gravity pulls the water down through the sand, the tiny sand particles catch any dirt and debris. At the bottom of the tank, the filtered water flows through the collector unit and out the outlet pipe.
Over time, the collected dirt and debris in the sand slows down the water flow. Pressure gauges are normally installed at the filter inlet and outlet to give an idea of the blockage level inside. If gauges show much greater pressure on the inlet pipe than the outlet pipe, this means that there is a build-up of dirt/debris in the sand. This means it's time to backwash the filter. To carry out a backwash, the water is redirected using the standard 6-way multiport valve supplied with all residential Filters or, in commercial applications, by adjusting the four or five-valve battery system (PVC ball or butterfly valves) which controls the water flow. To carry out the backwash, the return pipe leading to the pool is closed and the drainage pipe, which leads to a discharge area (such as a sewer system), is opened. By using the multiport valve or adjusting the valves in the system, the flow is redirected so that the water from the pump flows through what is normally the filter outlet. This reversal of the water flow means that water from the pump is pushed upwards through the sand, dislodging the dirt and debris. The dirty water then flows back through what is normally the filter inlet pipe and out through the backwash/drainage pipe.
In place of a sand filter, some pool systems use a diatomaceous earth filter or a cartridge filter. In a diatomaceous earth filter, water from the pool passes through filter grids coated with diatomaceous earth, a fine powder made from the chemically-inert, fossilized remains of sea organisms called diatoms. In a cartridge filter, dirty water passes through a filter made out of polyester cloth or corrugated paper. Instead of backwashing, you simply remove the filter and hose it off. Certain countries have laws that stipulate that entire volume of the water in the pool must pass through the filter in a certain amount of time – this can range from 30 minutes to eight hours and depends largely on weather conditions, frequency of use and bather load. Often, the pump and filter system is also connected to a well or municipal water line so fresh water can be added to the pool. This is necessary to replace water lost to evaporation, backwashing and "splash-out" (water that splashes on the deck or is carried out on people's bodies and swim suits).

Water Treatment

The pool filter does the majority of the work to keep the water clean, but chemicals are required to maintain the pool in optimum condition. The chemical balance of pools is important for the following reasons:

• Dangerous pathogens, such as bacteria, thrive in water. A pool filled with untreated water would be a perfect place for disease-carrying microorganisms to move from one person to another.
• Water with the wrong chemical balance can damage the various parts of the pool.
• Water that is not properly balanced can become murky or even irritate the skin and eyes.

In order to get rid of pathogens in the water, a disinfecting/sanitizing agent is reuiqred. The most common sanitizer is chlorine, which is a chemical compound available in a solid state, like calcium hypochlorite, or a liquid, like sodium hypochlorite. When the compound is added to the water, the chlorine reacts with the water to form various chemicals, most notably hypochlorous acid. Hypochlorous acid kills bacteria and other pathogens by attacking the lipids in the cell walls and destroying the enzymes and structures inside the cell through an oxidation reaction. Alternative sanitizers, such as bromide, do basically the same thing with slightly different results.
Chlorine is typically prepared in liquid, powder or tablet form (though some professionals use gaseous chlorine), and it can be added to the water anywhere in the cycle. Generally, chlorine is added to the return line after the filter by means of chemical feeder. It can also be added directly into the pool by placing tablets in the skimmers or inside floating chlorine-dispenser / chlorinators, but sometimes the chlorine tends to be too concentrated in those areas when done in this way. One problem with hypochlorous acid is that it's not particularly stable. It can degrade when exposed to ultraviolet light from the sun, and it may combine with other chemicals to form new compounds. Pool chlorinators often include a stabilizing agent, such as cyanuric acid, that reacts with the chlorine to form a more stable compound that does not degrade as easily when exposed to ultraviolet light. Even with a stabilizing agent, hypochlorous acid may combine with other chemicals, forming compounds that are not very effective sanitizers. For example, hypochlorous acid may combine with ammonia, found in urine, among other things, to produce various chloramines. Not only are chloramines poor sanitizers, but they can actually irritate the skin and eyes and have an unpleasant odour. The distinctive smell and eye irritation associated with swimming pools are actually due to chloramines, not ordinary hypochlorous acid -- a strong smell usually means there is too little free chlorine (hypochlorous acid), rather than too much. To get rid of chloramines, the pool needs to be shock-treated i.e. add an unusually strong dose of chemicals is added to clear out organic matter and unhelpful chemical compounds. The formation of chloramines is related to the second major element in pool chemistry, maintaining the right pH in the pool.

pH Level

The water's pH is a measure of its total acid-alkalinity balance -- the relative proportion of acids and alkalis in the water. Simply put, water that is either too acidic or too alkaline will cause undesirable chemical reactions. If the water is too acidic, it will corrode metal equipment, cause etching on the surface materials and cause skin irritation. If the water is too alkaline, it can cause scaling on the pool surface and plumbing equipment and can cloud the water. Additionally, both high acidity and high alkalinity alters the effectiveness of the chlorine. The chlorine won't destroy pathogens as well if the water is too alkaline, and it will dissipate much more quickly if the water is too acidic. On the pH scale, zero indicates extreme acidity, 14 indicates extreme alkalinity and 7 indicates a neutral state. The recommended pH-range for a swimming pool is between 7.2 and 7.8. To raise or lower pH, acids or alkalis need to be added to the water. For example, adding sodium carbonate (soda ash) or sodium bicarbonate (baking soda) will generally raise the pH, and adding hydrochloric acid (approx. 30% solution) or sodium bisulphate will lower the pH. Maintaining the proper balance of chemicals in the pool is a continual process, because any new element (oils from a swimmer's body, a shot of chlorine, stuff that falls in the water) changes the chemical composition of the water. If the pH is too high, not enough pool cleaning can take much longer than normal. Once the chemicals that make up the chlorine have cleaned the pool water, their residuals either combine with another chemical, such as ammonia, or are broken down into single atoms which renders the chlorine harmless. Sunlight speeds these processes up – that is why, particularly in warm climates like the Middle East, it is necessary to add chlorine to the pool more frequently than in other, cooler places. In addition to pH, the following levels should also be checked: total alkalinity, calcium hardness and total dissolved solids.
While the bacteria-killing properties of chlorine are very useful, chlorine also has some side effects that can be annoying to humans, and possibly even hazardous. Chlorine has a very distinctive smell that most find unpleasant, and some find overwhelming. There is also the "itch factor" -- chlorine can cause certain skin types to become itchy and irritated. The hypochlorite ion contained in chlorine can also cause many fabrics to fade quickly when not rinsed off immediately after exiting the pool.
There are other sanitizing systems available to disinfect the water in your pool. Although, many systems claim to be chlorine-free, many of them actually work in conjunction with chlorine to sanitize the pool. Effectively this means that the chlorine content in the water is reduced, thereby reducing the possible adverse side effects mentioned above. Many 'alternative' systems attempt to justify their purchase by touting a savings of "90% chlorine". Pool owners are even told to cut back on the pool chlorine level to prove this savings. Wrong!! Cutting back on the level of pool chlorine to save money is like using a credit card to conserve cash it works fine until the bill appears and the true cost becomes known. The same goes for reducing chlorine levels. The water may look fine for a while (how long depends on bather load) but when the filter cycle shortens and the water becomes turbid, a good chlorine shock will be required ... some great savings! The true test for chlorine savings is not by reducing FAC levels but by maintaining your standard levels to see if the alternative system being tested will maintain these levels with a 90% reduction of chlorine usage!

What Makes Chlorine Unique?

Chlorine (bromine is similar and for brevity will not be further mentioned) has a list of properties that make it an ideal sanitizer for pools/ spas. Let's look at these properties.
Sanitizer: Free available chlorine (FAC) (hypochlorous acid) is a sanitizer. It enters through the bacterial cell wall and kills the organism by destroying the sulphur groups on the cell's enzymes, causing the cell's metabolism to stop, resulting in the cell's death.

Fast Kill Times: Not only does FAC kill bacteria - it does it very quickly. The Association of Analytical Chemists uses a kill time of 30 seconds at 0.6 ppm FAC to completely destroy a given concentration of bacteria as a standard for a swimming pool disinfectant.

Stable Residual: FAC is stable enough in solution to allow a residual to exist in every portion of pool water. Such FAC residuals "stand guard" against the presence of bacteria which will be quickly destroyed.

Oxidizing Agent: While not the most vaunted property of chlorine, its ability to oxidize is the key to its usefulness as a sanitizer. It has been estimated that over 90% of the FAC residual is used to oxidize organics introduced into the pool by bathers. if the purpose of FAC was only to kill bacteria, much lower levels of chlorine could be allowed. it is the oxidative properties of chlorine which make it the workhorse of cleansing pool/ spa water.