Troubleshooting Pool Water
If the swimmers complain about burning eyes and nose, or dry, irritated skin, there is most certainly a problem with the pool water chemistry.
This could be caused by various factors:
the pH is too high or too low;
the total alkalinity level is too low;
the calcium hardness level is too high.
By testing the swimming pool water and correcting these levels, the problem should disappear. Even at the recommended levels, chlorine can cause eye irritations. To enable effective sanitation at lower chlorine levels, consider installing a mineral pool sanitiser (e.g. Pool Wizard) which requires only about 25% of the chlorine normally necessary.
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 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 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 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.
After testing the water, the necessary chemicals must be added to bring the pH to a level of about 7.2 .
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 write to us for more detailed instructions on how to reduce it. The quantities of hydrochloric acid and dry acid you will need can be calculated using our pool calculators.
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.