Water Testing - The Rules
At Pool Supermarket, we take testing your pool or spa water seriously. We have over 10,000 registered customers that use our FREE water testing service every year. They keep coming back because we won't fill you with arm fulls of chemicals you don't need or will never use. Honesty is the best policy. If your pool is well balanced & doesn't need chemicals, we will be as happy as you. If you would like us to test your pool or spa water, we ask that you follow the directions below. This helps us to accurately & correctly balance your pool.
- We only test water that comes in a clean sample bottle. If you don't have one visit our store to receive one FREE of charge!
- Please have the filter running for a few hours before taking your sample. Take the sample from down below the surface.
- Please completely fill the sample bottle.
- DON'T put chemicals in the pool & then take a sample. This will only give us a false reading
- Please let us know if your pool is not quite right. We have seen pools you could walk on, so we CAN fix your problems.
Water Testing - DIY
Some people may prefer to test their pool water themselves. We cater for you also by providing you with advice and a large range of test kits, test strips and replacement chemicals.
Below are the basics of Pool Chemistry. Please ask us for anything you may not understand.
Why is the pH so important in my pool?
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 ideal pH for a Fiberglass Pool is 7.0 whilst in other pools, Marble sheen, Concrete, Peblecrete & lined Pools the pH should be 7.6.
What happens if my pool is too acidic? (If my pH is too 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 sanitised, 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 if my pool is too Alkalai? (If my pH is to 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 disinfection you need.
- In alkaline swimming pool water, the swimmers suffer too. Our eyes and nose burn and our skin gets dry and itchy.
By neglecting to test and correct the pH of swimming pool water, we not only cause it to become unsightly, but we also cause ourselves physical discomfort. In addition to this, we insist on throwing away our hard-earned money on swimming pool chemicals that cannot possibly be effective in that pool water.
To raise the pH level we use sodium carbonate (SODA ASH).
To lower the pH Acid, either liquid or dry, is added to the pool .
What is 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. 120 Being Ideal
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, Marblesheen 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 your sanitiser.
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.
Lowering the total alkalinity is also a slow process. Acid, either liquid or dry, is added to the pool in small amount each day. It could take days or even weeks to reduce the TA if it is very high.
Testing the chlorine
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:
- Free available chlorine (or residual chlorine) - is the amount of chlorine in the pool that can sanitise or disinfect the water and is the important measurement for us.
- Combined chlorine - consists of undesirable, bad-smelling, irritating compounds which form when there isn't enough free available chlorine.
- 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 disinfection.
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.
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.
If the stabiliser level is too high, try using a non-stabilised chlorine product until the level falls to the recommended limits.
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.
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.
Copper, Iron and others
Copper is one of nature's elements. It is also used in the equipment and plumbing in most swimming pools. Copper, in its free state, may also be present in cheaper algaecides.
Corrosive water (low pH, low TA, low calcium hardness) caused by improper water balance or misuse of chemicals can cause copper to be dissolved into the pool water. The water supply you use for topping up the pool may also contain high levels of copper, iron and other metals.
The maximum level for copper is 1.0ppm, though lower levels are recommended. At high concentrations, the copper deposits out of the water and onto hair, fingernails or pool walls causing green stains. High levels of copper can also cause green water.
Iron in the pool causes the water to turn brown or green. It can also cause staining of the pool walls. Iron has much the same causes as copper (i.e. corrosive water or high levels in the top-up water). The maximum level of iron is 0.3ppm although iron-free water is desirable.
Copper and iron can be "locked" into the water using chemicals (chelating agents). This prevents the metal from dicolouring the water or staining the pool.
Magnesium and manganese in the water increase the hardness and can cause scale. See also calcium hardness.