By Watermaid

Perhaps the most common problem associated with swimming pools is algae. This information will help you understand some of the problems involved in dealing with algae in swimming pools.

There are some 24,000 known types of algae and they are all distinguished by being single celled organisms, capable of photosynthesis, mitosis and meiosis. That is, they produce their own food. All cells can divide and reproduce by combining with other algal cells. In swimming pools the ideal environment can exist where there are periods of zero chlorine. The problem for pool owners is the short life cycle of algae; sometimes as low as twenty minutes. Under normal growth algal blooms can take less than a day to mature into a green pool. At the first sign of adversity, the algae population go into a reproduction phase where two cells meet, parley and combine to produce eggs or spores. The size of the spores is less than 0.2 microns. DE filters filter 5 microns and above and sand filters 20 microns and above. Algae will die from chlorine with concentrations as low as 0.05ppm but spores can resist chlorine levels of up to 10ppm. Normal daily chlorine dosing does not achieve those conditions. A manual chlorine dose would need about 1–2 Kg of calcium hypochlorite equivalent to be effective. Spores, however, cannot tolerate copper salts, as copper attaches to the shell or (endospore) preventing germination.

We advise that the first step should be to lower the pH (generally by the addition of up to 2 litres of pool acid) and then followed, about 4 hours later, with a copper treatment to attain a 1ppm copper level in the pool. 70 grams (about 1 heaped tablespoon) of copper sulphate dissolved in 10 litres of water spread around the pool is the most economical method, but the use of any commercial copper based algaecide will do. Lowering pH is an essential part of reducing algae resistance.

After about 12 hours a pool, broom or brush (non abrasive to the surface), and a garden hose fitted with a jet spray (available at all hardware shops) can be used to remove algae from the walls.

The next step should be to use flocculent in the pool. Overnight it will settle on the pool floor as a blanket of debris which should then be vacuumed directly to waste and NOT through the filter. After this treatment, a pool should attain its clear clean condition within several days of constant filtration and adequate chlorination.

Finally, we strongly recommend the use of Lanthanum Carbonate (Antialgas) to reduce the phosphorous content to less than 1 part per billion. This starves algae of an essential element for growth.


Maintain: pH between 7.2~7.8 – Chlorine 0.5~ 3ppm Max. Ensure: Chlorine stabiliser is less than 100ppm to enable the Chlorine to work effectively.

Algae breed in sunlight – more as the pool temperature rises. To inhibit algae growth, run your pool filtration when the sun has gone down for the longest time, 6~10 hours summertime (when temperatures drop and you are not using the pool e.g. winter time, the time clock can be set much lower) and a couple of hours during the day, AND, always when there are people in the pool – people are the biggest contaminants in a pool apart from animals –- dogs can pollute a pool twelve times as much as a human.

Information supplied by:

Watermaid S.L.. Suppliers and importers of swimming pool automatic systems

Saltwater Chlorination ~ pH control ~ Heat pumps


Information: JB Supplies/Information

Tel: Dave 636 698 501 / Mark 646 705 088