Algae growth can be treated - Watermaid shows how

Algae Growth Control in Private Swimming Pools

Algae are free floating microscopic plants and animals known as Plankton and are divided into many classes. They are found in the free floating and clinging varieties. The clinging type will form algae growths and embed itself into pores and crevices in concrete and between tiles and is the more persistent type.

Whenever water is exposed to air and sunlight, algae will gain access in the same manner as weeds grow in a garden.

If conditions are favourable, profuse algae growth of great variety and many colours will develop.

Sunlight is essential to algae growth as well as carbon dioxide (CO₂), mineral matter and suitable temperature. Organic matter in the water does not have much influence as a food. Temperature plays an important part in the type of algae that grows at that particular time and there are types that grow in winter conditions as well as summer. However, the summer growths are usually more active and are probably due to the presence of longer sunlight.

The presence of algae in the swimming pool will develop turbidity, produce odour and taste in the water and will necessitate more frequent backwashing due to their clogging action on filter beds.

Algae growths are objectionable in appearance. As they are slimy they are the cause of most accidents in and around a swimming pool because of this slippery nature. They also create a high chlorine demand should heavy growths develop; these growths then tend to foster bacterial growth and retard the action of chlorine. They also give rise to odour problems when reacting with chlorine.

These conditions in a swimming pool are an indication that regular free chlorine residual is not being maintained in the water. Provided a free chlorine level is maintained at all times, algae growths will not appear. However, should these conditions develop and heavy growths become established, the chlorine demand is increased to a point where the ordinary levels of free chlorine residuals will not kill them off. It is then necessary to apply super chlorination, e.g. maintaining a free chlorine level of 10 ppm or over during the night when the pool is closed to bathers. This is the most effective treatment and next day it will be found that the dead algae will brush or slough off quite readily.

This can be achieved by adding 1½ lbs. of calcium hypochlorite 70% to 10,000 gallons of water.

However, with stabilized pools using cyanuric acid, the problem is getting rid of the high chlorine level before bathing commences. This can be achieved by de-chlorinating next morning by adding sodium thiosulphate (photographic "hypo") at the rate of 2 lbs. per 10,000 gallons. Sodium sulphite or sodium bisulphite can also be used to de-chlorinate.

At pH levels below 8.0 most waters contain increasing amounts of carbon dioxide necessary for their growth; with waters above a pH 8.0 the amount of carbon dioxide becomes negligible and this, together with chlorine will reduce the incidence of algae trouble.

There are also a number of other chemicals that are sometimes added to water as algicides. They act in two ways; one to prevent growths (algistatic) and the other to kill growths (algicidal). In most cases the amount required to kill a growth in four hours may be 3 - 8 times greater than that required to prevent one forming within ten days.

The most common algicide that has been used over the years is Copper Sulphate (CuSO₄5H₂0). The normal dose is in the region of 1 -2 ppm. However, if the growth is well established, higher rates will be required.

The difficulty involved in using copper sulphate in swimming pools is that the effective portion, copper, is precipitated out of solution by the bicarbonate content of the water and rendered ineffective, usually in a period of 5 - 7 days and is removed in filtration. Another side effect is that in conjunction with chlorination, the compound formed may discolour bathing costumes and turn hair green.

Another most effective metallic salt which will kill algae in a few minutes at 1 ppm is phenyl mercuric acetate. However, as this is a highly poisonous material to handle, it is not recommended for swimming pools.

Newer ones have come on the market in recent years: the amine types and the quaternary ammonia compounds such as Rosin amine D. acetate, Cetyl trimethy ammonium bromide, lauryl pyridium chloride, etc.

When evaluating algicides, it is probably most important to know whether the concentration recommended for the product is to prevent growths of algae (algistatic) or it will kill established growths (algicidal). In most cases there will be a loss of algicide as the water is continuously filtered due to absorption on sand or diatomite of the filter bed and it is usual after the initial dose to follow up with smaller weekly doses.

Some algicides possess a high chlorine demand and therefore rob the water of its chlorine residual. Others cause severe frothing in the water and in the filters.

It should also be noted that some strains of algae will build up a resistance to some types of organic algicides.

Porous surfaces or cracks in a swimming pool make it difficult to control or eliminate it as the spores may be protected by the "dead" water in the porous structure and will readily give rise to spontaneous development should the free chlorine level in the water be lost for any length of time.

During winter months when the pool has been left full of water and without treatment, this problem can be quite alarming before the start of the next swimming season. To prevent or minimize it, it is recommended that at the close of the season the pH of the water should be raised to 8.3 in order to lower the level of dissolved carbon dioxide. At intervals of approximately a month, depending on the visual observation of the development, the plant should be turned over during the night and super chlorinated with chlorine. Another alternative is to cover the top of the water, by floating black polythene sheet and thereby eliminating sunlight necessary for growth.