Swimming Pool Algae

By far the most regular complaint of swimming pool owners is algae. This is because the algae is visible and unsightly. There are over 21,000 species of algae known to man but only a fraction of these are encountered in swimming pools.

Algae does not cause disease. It is a plant that turns sunlight and carbon dioxide into food and provides nutrients for bacteria which can then multiply rapidly (and may cause illness). When there is algae present in the pool water, the chlorine is used up rapidly trying to combat its growth. This process has a tendency to raise the pH, thus decreasing the efficiency of the remaining free chlorine.

Unchecked algae growth can turn the swimming pool cloudy or makes the pool water green and results in foul odours and tastes. Black algae, which is more difficult to control than green or blue-green algae, can also stain the swimming pool's walls and floor.

Prevention is better than cure. Adequate levels of free chlorine will prevent algae from growing out of control. When algae growth is noticed, it requires harsh treatment. Usually shock treatment with chlorine or an algaecide is recommended. If the pool has a mineral sanitiser such as the Pool Wizard installed, algae growth is a sign that you need a refill. Algae cannot grow in water sanitised with the Pool Wizard, provided the water is properly balanced.

Waterborne Pool Illnesses

Swimming pools are exposed bodies of water and are thus subject to contamination. The contamination can be carried into the pool water by the environment (e.g. wind, rain) or by swimmers.

There has been a dramatic increase in infections and infectious diseases from swimming pools over the past few years. Some strains of bacteria and viruses have built up resistance to the chlorine we use as a sanitiser in our swimming pools. Others are destroyed very slowly. Consequently, there has been an increasing demand for alternative sanitisers able to quickly and effectively destroy the disease carrying organisms.

Unfortunately, it is impossible to prevent bacteria and viruses from entering the pool water. In swimming pools with a high swimmer load, the level of contaminants entering the water are especially high. Ill or recovering people are requested to abstain from swimming, but many ignore this plea. Chlorine breaks down very fast in the presence of high contamination and swimmer load and due to the effects of the sun's UV rays and heat. With these factors in mind, many swimming pool maintainers over-chlorinate the pool water in the hope that illness can be prevented.

This creates another dilemma - chlorine, too, can cause health problems and overuse should be avoided at all costs. Mineral water sanitisers such as the Pool Wizard can reduce chlorine consumption by 75%, thus creating a safer and healthier swimming environment. The Pool Wizard also effectively destroys potentially harmful bacteria, viruses and algae before they can strike.

A total reliance on chlorine for swimming pool disinfection is illogical in the light of research results. There is unequivocal proof of the efficacy of non-chlorine additives or pool water treatments that can supplement chlorine to create safer pool water. Elements such as copper and silver have become widely accepted as potent anti-bacterial and anti-viral agents. Patented products like the Pool Wizard make good use of this knowledge in producing swimming pool disinfectants able to cope with the micro-organisms that chlorine cannot destroy.

These are some of the diseases that can result from infected pool water:

Below are some references to illnesses resulting from swimming pool water:

Cloudy Swimming Pool Water

Clear, sparkling pool water is a joy to look at. A cloudy swimming pool loses its beauty and becomes uninviting for swimmers.

Cloudy swimming pool water can result from one of several factors:

  • the pH is too high;
  • the total alkalinity level is too high;
  • the stabiliser level is too high;
  • the chlorine level is too low;
  • the calcium hardness level is too high;
  • the level of total dissolved solids is too high;
  • there are high levels of metals (discoloured pool water);
  • there is a lot of pool algae growth;
  • the filter needs cleaning or servicing;
  • there is a large quantity of microscopic particles in the pool water.

By testing and correcting the above, the cloudy pool water problem should disappear.

Burning Eyes and Nose

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.

Pool Chlorine Smell

Many pool owners complain that the swimming pool water is not really clean, but they can smell the chlorine so there must be enough in the water to ensure disinfection.

Unfortunately, if you can smell chlorine, the swimming pool hasn't got enough - strange, isn't it?! What you can smell are chloramines. These are formed when insufficient levels of free available chlorine react with ammonia and other nitrogen-containing compounds (swimmer waste, sweat, urine, etc.), resulting in their only being partially broken down (creating halomethanes).

To confirm this, measure the free available chlorine and total chlorine. You will be able to calculate the unwanted, irritating combined chlorine compounds as follows:

Combined chlorine = total chlorine - free chlorine

You will probably find that there is little or no free available chlorine and too much combined chlorine. A chlorine shock treatment or other pool water sanitiser is necessary to complete the disinfection and dissipate the combined chlorine.

The combined chlorine in the pool water can also be destroyed with a non-chlorine shock if you prefer not to use large quantities of chlorine.

Staining of the Swimming Pool

Stains can, and do reduce the attractiveness of a swimming pool. By regularly testing and maintaining the water chemistry of a pool, we can avoid pool problems such as staining. The cost of regular pool water maintenance is far lower than the cost of stain removers, acid washing or swimming pool resurfacing.

Staining of the swimming pool's surfaces does not result in illness, but has a negative aesthetic effect on the bathers at the swimming pool. The swimmers have the impression that the swimming pool looks dirty and this detracts from the swim.

Staining can result from several factors:

  • the pH is too low;
  • the total alkalinity level is too low;
  • the calcium hardness level is too low;
  • the level of total dissolved solids is too high;
  • there are high levels of metals.

By testing and correcting the above pool water parameters, the staining should stop. Existing stains will, however, still require special treatment and we suggest you consult a pool professional.

Balancing pool water chemistry

According to the results of the pool water tests, we may need to add chemicals to bring the pool water back into the ideal balance for swimmer safety and visual clarity.

We are required to regularly adjust the pH and chlorine levels as these tend to fluctuate according to the weather conditions and swimming pool use.

It is extremely important to adjust the pH before adding the chlorine. When the pH is 8.0 the chlorine is only 20% effective and at a pH of 8.5 the chlorine is only 8% effective. Chlorine becomes overactive when the pH is lower than 7.0.

Despite a balanced pool water system, the swimming pool can sometimes become cloudy and lose its sparkle. This is usually a result of minute suspended particles of dirt in the water that are too small to be trapped in the filter. These particles can usually be cleared using a flocculant/coagulant, which clumps them together, allowing them to be removed from the pool. One of the effects of the Pool Wizard is a coagulant action, making the use of flocculant or coagulants redundant when a Pool Wizard is installed.

Adjusting pool water pH

Assuming that the total alkalinity level is correct, we adjust the pH according to the results of the pH test. Most better test kits have an acid demand test, which allows you to calculate the amount of acid to add in order to correct the pH. You generally need to know the volume of the pool to calculate the quantity required.

In general, the pH of pool water tends to rise. This is a result of chlorination, swimmers wastes (sweat, urine, ...) and nature's tendency to balance the pH of standing water at about 8.5.

High pH can be reduced with an acid. The most common pool acids are:

  • liquid hydrochloric acid (muriatic acid) and
  • dry acid (sodium bisulphate).

Extreme care must be taken when adding acid to the pool, as negligence can result in serious burns. Before adding the acid, be sure there are no swimmers in the water and that the pump is running. You will need a plastic bucket to mix the acid in.

Always add acid to water; never add water to acid! 3/4 fill the bucket with water from the pool. Add the acid to the bucket and pour itslowly around the deep end of the pool. If you are adding a large quantity of acid, do it in stages - DON'T add large amounts of acid to the pool at one time. Allow the pump to circulate the water for at least 4 hours and then test the pH again. A pH reading of 7.0-7.6 is required, with 7.2 being the ideal level.

If you add too much acid to the pool at one time, you risk etching the walls, corroding the pipes and pump fittings and you lower the total alkalinity of the water.

Low pH is increased with an alkali - this is most commonly soda ash (sodium carbonate). The amount of sodium carbonate required to raise the pH can be obtained from our soda ash calculator.

Adding chlorine to pool water

Assuming that the total alkalinity is at the right level and the pH is correct, chlorine can be added. The amount of chlorine to add depends on the present chlorine level and the type of chlorine used. Refer to the manufacturers instructions for quantity. If you need to know the volume of water in the pool, you can work it out using our volume calculators.

As discussed previously, chlorine degrades rapidly under the influence of UV light. For this reason chlorine should be added only in the late afternoon or early evening, when it can dissolve and mix thoroughly before the damaging sun's rays can affect it.

The chlorine should be evenly scattered/ poured around the pool or poured slowly in front of the return flow jets to ensure rapid and even distribution.

Chlorine should be kept at a level of 1.0-3.0 ppm to ensure sufficient sanitation. If you are using a Pool Wizard, a level of 0.5 ppm is required. This combination will provide a far superior sanitation to chlorine alone.

If the pool has very high levels of contamination or there is a strong smell of chlorine around the pool, you may need to shock treat the water. This involves adding large quantities of non-stabilised chlorine (or non-chlorine oxidisers) to the pool, which rapidly destroys the offending matter.

Flocculation in swimming pool water

One of the problems with our easily maintained sand filters is that they are unable to trap dirt or foreign matter below 0.02 mm (20 microns). Cloudy water is probably a result of these minute particles of matter if the total alkalinity, pH, calcium hardness and TDS are all within the recommended limits.

Flocculation (or coagulation) is the process of adding chemicals which bind or stick these tiny particles together, resulting in larger clumps which settle to the bottom of the pool and leave the water clear. These "clumps" can be easily removed by vacuuming the floor of the pool.

Chlorination or chlorine shock treatment may also clear the water, but this is both expensive and upsets the water balance.

Flocculant is relatively inexpensive and can be used frequently in pools that are exposed to high levels of pollutants (both environmental and swimmer waste). Follow the manufacturer's instructions for use, as there is a wide variety of "floc agents" available, each of which has different directions.

Adding stabiliser (cyanuric acid)

If the stabiliser test shows that the level is low (below 30 ppm), stabiliser needs to be added. The quantity can be determined from with our stabiliser calculator.

New pools and pools that have been drained need to be stabilised. Existing pools usually only require a top up of cyanuric acid. Never neglect the stabiliser, or you will waste huge quantities of chlorine.


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 discolouration, 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.