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Ph Level

The pH is one of the most important factors in pool water balance and it should be tested and corrected at least every week. pH is the measure of how acid/ alkaline the swimming pool water is. A pH of 7.0 is neutral - below 7.0 is acidic, above 7.0 is alkaline. The pH of our eyes is 7.2 . No wonder that the ideal pH for your pool is just that - 7.2 , and should be kept within the range of 7.0-7.6 .  

What happens when the pool is too acidic?
(pH is low)

• If your swimming pool is Marbelite or plaster, the pool water will begin to dissolve the surface, creating a roughness which is ideal for pool algae growth. A similar result occurs in the grouting of tiled swimming pools.
• Metals corrode - and this includes swimming pool equipment, pipe fittings, pump connections, etc.
• As the swimming pool walls and metal parts corrode, sulphates are formed. These sulphates are released from the water onto the walls and floor of the swimming pool causing ugly brown and black stains.
• Chlorine, which is used as a disinfectant in the swimming pool water, is activated and lost to the atmosphere very quickly. The water is not being sanitized, and we are throwing away our money by adding chlorine when the pH is too low.
• When we swim, our eyes and nose burn. Our swimwear fades and perishes. Our skin gets dry and itchy.  

What happens when the pool is too alkaline?
(pH is high)

• The calcium in the swimming pool water combines with carbonates and forms scale, just like in our kettles. This calcification is seen most at the waterline, where it traps dust and dirt, turning black with time.
• The swimming pool water starts to become cloudy or murky and it loses its sparkle.
• The calcium carbonate has a tendency to plate out on the sand in the swimming pool filter, effectively turning it into cement. So your sand filter becomes a cement filter, and loses its ability to trap dirt from the pool water.
• As the pH rises, the power of the chlorine to act on foreign particles is lost. At a pH of 8.0 the pool can only use 20% of the chlorine you put in. So 80% of it goes to waste and you would need 5 times as much chlorine to provide the disinfections you need.
• In alkaline swimming pool water, the swimmers suffer too. Our eyes and nose burn and our skin gets dry and itchy.

Chlorine Level

When planning to buy a test kit to measure the chlorine levels in your pool, it is important to remember that there a 3 aspects which can be measured:

1. Free available chlorine (or residual chlorine) - is the amount of chlorine in the pool that can sanities or disinfect the water and is the important measurement for us.
2. Combined chlorine - consists of undesirable, bad-smelling, irritating compounds which form when there isn't enough free available chlorine.
3. Total chlorine - is the total amount of chlorine in the water. It includes both free available and combined chlorine.

We are interested in how much available chlorine there is in the water - chlorine that can act on foreign substances in the water to keep the pool clean and safe for the swimmers.

Too little chlorine results in algal and bacterial growth, waterborne illnesses, cloudy water and insufficient sanitation of the water.

Too much chlorine can result in eye, nose and skin irritations. Remember, too, that the chlorine in the pool is carcinogenic and we should aim to keep its level to the minimum required for complete disinfections.

Test kits which use tablets rather than liquid reagents are preferred. The tablets are easier to use and provide more accurate results. Also make sure that the chlorine measuring tablets are "DPD" as only these can measure the free available chlorine.

Take the water sample from at least 20-30 cm below the surface and at least that far from the wall of the pool. Test the water according to the test kit's instructions.

The desirable level of available chlorine in the pool is 1.0-3.0ppm with 2.0ppm being the recommended ideal. If you are using a Pool Wizard, the ideal free chlorine level is 0.5 ppm (25% of the chlorine required in pools without a Pool Wizard).

Add chlorine according to the test results. As a rough guide, a pool needs about 600 grams of granular chlorine (2-3 cups) for each 50,000 litres of water twice a week during the hot swimming season (150 grams or 1/2-3/4 cup if using a Pool Wizard). Please note that this is only a guide, and actual chlorine requirements can only be determined by regular testing

Total Alkalinity

The total alkalinity (TA) is a measure of how much of the alkaline substances there are in the water. In the swimming pool water, we are concerned with bicarbonate alkalinity, which should be between 80 ppm and 120 ppm.

When the total alkalinity (TA) is within this range, it prevents rapid pH changes and "stabilises" the pH level.

If the TA is too low, Marbelite and plaster walls will become etched, metals corrode, the pool's walls and floor can stain, the water can turn green, eyes burn and we can have pH bounce (pH rapidly going up and down, seemingly at random).

If the TA is too high, the pH is difficult to adjust, the water becomes cloudy, the pool constantly needs acid (according to your test kit) and the chlorine loses its efficiency as a disinfectant.

It is recommended that you test the TA regularly, but in practice it changes very little in a well-maintained pool.

To raise the level of TA, we use sodium bicarbonate; it is the only chemical which will do this without increasing the pH very much. Use the calculator to find out how much sodium bicarbonate you need to raise the TA of your pool. Note that you should only add sodium bicarbonate at the rate of 1 kg per 50,000 litres of water every 4 days. Raising the TA can therefore be quite a time-consuming, slow process.

Lowering the total alkalinity is also a slow process. Acid, either liquid or dry, is added to the deepest part of the pool with the filter off. The acid should only be added a little at a time, diluting it before pouring it into the pool. Wait 3 days between applications. It could take days or even weeks to reduce the TA if it is very high. You should consult a pool professional if you have a high TA, or you can visit the Total Alkalinity forum for help on how to reduce it. The quantities of hydrochloric acid and dry acid you will need can be calculated using our pool calculators.

Calcium hardness

Total hardness in the context of pool water refers to the total mineral content of the water. This is made up of calcium, magnesium, iron, manganese and other elements. These elements are present in the water used to fill the pool, and the levels can increase through the use of regular pool chemicals (e.g. chlorine composed of calcium hypochlorite). We are interested in the calcium hardness levels.

The ideal range for calcium hardness is 250-350 ppm.

If the calcium hardness is too low, the water becomes corrosive and results in the etching of the pool's surfaces. Metals corrode - and this includes pool equipment, pipe fittings and pump connections. As a result, the pool's walls and floor can stain.

Low calcium hardness can easily be increased using calcium chloride. The amount needed can be calculated using the calcium chloride calculator.
NOTE: divide the required amount of calcium chloride into 3 parts. Add the first part and circulate the water for at least 4 hours. Test the water again and repeat the process until the desired level is reached.

If the calcium hardness is too high, the result will be scale formation on all pool surfaces. The filter and pipes become clogged, reducing water flow and filtration efficiency. The water becomes cloudy and swimmers complain of eye irritations.

Reducing calcium hardness is very difficult. Either replace some or all of the water in the pool, or add chemicals that will keep the calcium in solution and prevent it from depositing out. If the calcium hardness is high, we recommend that you consult a pool professional  

TDS problems

Total dissolved solids (TDS) is, as its name implies, the measure of the total amount of dissolved material in the water.

The level of TDS in the pool is influenced by many factors; the chemicals we add to adjust the pH, chlorine, water hardness, alkalinity, dust, dirt, human waste, . . . all increase its level.

The maximum acceptable level of TDS for swimming pools is 1,500 ppm. At values above this, we begin to notice stains in the pool. It will also reduce the activity of any chemicals you add, preventing them from doing what they're supposed to. The water may also become cloudy.

Unfortunately, if the TDS level is too high, there is little that can be done to reduce it. The only practical solution is to drain some or all of the water from the pool (depending on how high the TDS is), and replace it with fresh water (with a low TDS). A regular backwashing routine will help to prevent the TDS from rising too much.  

Chlorine, which we use as a sanitiser in our pools, is very unstable.The effects of the sun's UV rays and high temperatures reduces chlorine's effectiveness and breaks it down into inactive components.

Stabiliser, or cyanuric acid, is a compound which protects the chlorine from the negative effects of UV and heat. It not only ensures that our pool remains clean and safe for the swimmers throughout the day, but it also reduces the amount of chlorine we need to add in order to maintain these levels of disinfection.

"According to research results, pools without stabiliser lose about 90% of their total chlorine residual on a sunny day in two or three hours. Pools treated with 25 to 50 milligrams per litre of cyanuric acid, however, under the same conditions, lose only 10 to 15 percent of their total chlorine." (White et. al. , 1972)

Ideally, the stabiliser should be maintained at a level of about 50 ppm, the acceptable limits being 40-80 ppm. If you use a stabilised chlorine product, you will need to add very little, if any, stabiliser. To find out how much cyanuric acid your pool requires to raise the level of stabiliser, you can use our stabiliser calculator.

Algaecide

  The use of algaecide to prevent or destroy algae is often recommended. Its use, however, can result in water foaming, a change in total alkalinity and pH, and an increase in TDS. Cheaper copper-based algaecides can cause water dicolouration, staining of the pool walls and floor, and green hair and fingernails (see copper for more information). Algaecides that contain isolated (chelated) copper are desirable, though they tend to be quite costly. With the use of various sanitising units available, such as the Pool Wizard, algaecides are not necessary. If you use an algaecide, follow the manufacturer's directions.

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