Swimming Pool Water Treatment

Swimming Pool Water MaintenanceSwimming pools require regular maintenance during swimming season, up to three hours per week. Part of that time is spent vacuuming the pool, cleaning out leafs and other foreign debris from pump strainers, filters and skimmers and hosing down the decks, but a big part of the maintenance is staying caught up on your water treatment and balance upkeep.

You may not have the time, energy or expertise to do all this and might choose to hire a pool maintenance company for this, but knowing what is involved will help you understand what you are paying for.

To make the water in your pool fit for swimming, there are several factors to consider; disinfection (usually chlorination), pH, total alkalinity, and calcium hardness.

Water pH Balance

It is recommended that the pH of a swimming pool’s water be between 7.2 and 7.6, on the pH scale, which is slightly alkaline. The ph balance of a pool should be adjusted before you add chlorine. This is because chlorine’s sanitizing function is most effective at the proper pH level; if the water is overly alkaline, then the hypochlorous acid formed by the chlorine will have much less of a disinfectant effect, and more will need to be added. So you save money by adjusting pH first.

Acid or alkali products are added to the pool water to adjust the pH. Alkali products like sodium bicarbonate are to raise pH, acid products to lower pH include sodium bisulfate and muriatic acid. Use caution when adding acids to a pool as they can burn skin and be toxic; avoid splashing, wear gloves and goggles when dispensing, and wash any spills from skin, clothing and other materials immediately.

Pool water test kits are available at pool supply retailers. Get one that measures residual chlorine, pH, total alkalinity and hardness, you will need to do all this anyway. The tests are done by collecting a sample of water, dropping a reagent into the sample, and analyzing the reaction by comparing the result to a color chart.

Total Alkalinity

Total alkalinity is a measurement of the total amount of alkali compounds in the pool’s water. It includes carbonates, bicarbonates, hydroxides and other soluble alkali compounds. The water’s resistance to large fluctuations in pH levels is dependant on the total alkalinity level. Higher is better with this variable.

The total alkalinity of your local water will dictate how much adjusting you need to do, as it varies quite a bit from one part of the country to another. Generally a good total alkalinity to shoot for is in the range of 50 to 150 parts per million (ppm).

If the pH a pool tends to go up over a period of time, the target total alkalinity should be adjusted to between 50 to 80 ppm, and if the pH goes down, the total alkalinity should be between 80 and 125 ppm. When you have the alkalinity just right, the pH will rise or lower at a much slower rate, in other words, be stabilized.

Pool Disinfection

Proper disinfection of your pool is needed for it to stay clean and germ and bacteria free. There are a few options to choose from for pool sanitization.

Although bromine is becoming more widely used, by far the most prevalent pool sanitizer is chlorine. Bromine, which comes in tablet or powder form, has the advantage of not causing eye and skin irritation; it also does not have the powerful smell that chlorine does. However, bromine is more expensive than chlorine, needs to be added to the water in greater concentrations, and can become destabilized by sunlight.

Chlorine is the standard for pool disinfection and is the most recommended by pool specialists and health authorities. It is available in the form of liquid, gas, powder and tablet for rapid reduction of organic and disease carrying organisms.

When chlorine is added to a pool initially, some of the amount is consumed by the process of eliminating bacteria, contaminants and algae in the water, and a certain residual amount remains; the level of this residual chlorine must be maintained in order to control any new organisms introduced into the water by swimmers, wind, rain and other means. The level of residual chlorine should be kept at between 1 and 1.5 parts per million.

Saltwater pools are touted as an alternative to chlorine pool disinfection. It is still necessary to use a chlorine generator in these pools. The generator reacts with the salt in the water to generate chlorine through the process of electrolysis. Salt in the pool water is not lost through the chlorine generation process, so salt does not need to be added continually. The resulting chlorine does not have the harsh bleach smell and effects of chlorine tablets, and the water has a softer feel.

Calcium Hardness

Calcium hardness is a measurement of the level of calcium compounds dissolved in your pool’s water, and thus it’s hardness or softness. This needs to be monitored and adjusted because water that is too soft will leach plaster from your pool’s liner, causing pitting and also corrode metal in it’s equipment. Pool water that is too hard, that is, contains too much calcium, will lead to scaling and deposits on pool surfaces, filters and pipes.

The level of calcium hardness, most experts agree, should be between 200 to 500 ppm. By adding calcium chloride to the water, it’s hardness can be adjusted upwards, and by adding anhydrous trisodium phosphate, or diluting with fresh water, the hardness can be lowered.


All four of these factors are interrelated, and adjusting one will have an effect on the others. For any given levels of pH and calcium hardness, there is a corresponding level of total alkalinity at which the water will be balanced. A quick look at a Langelier-Based water scale will illustrate this. For instance, if you have tested your pool’s water at a pH of 7.6, and your calcium hardness at 300, then a total alkalinity of about 85 ppm will be required to achieve a balance.

When the water in a pool is balanced, it becomes much more stable and will tend to stay in balance longer. You will still need to do regular maintenance on it, because of changes due to evaporation and rainwater, but it will be easier to keep everything as it should be.

Photo by Lee Coursey, Creative Commons Attribution License