This is the most common problem and the simplest to solve. Algae grows in a pool when the water is not treated properly and there is a chemical imbalance. The reason we chlorinate pools is to keep the water clean, healthy and safe for swimming. Often the water in a well treated pool is cleaner than your tap water. Algae will tend to occur in warm water, sheltered areas or corners of the pool more easily. This is because chlorine evaporates out of warm water faster and the algae grows well in warmer conditions. Sheltered areas or corners of the pool can grow algae because of an insufficient flow of water or lack of sunlight to kill algae. The easiest way to stop algae growing is to keep the pH of your pool between 7.0 and 7.2 and keep the chlorine level between 2.0 and 3.0. Algaecides are often handy aids in preventing the occurrence of algae in your pool. If you have a salt water chlorinator you are not immune to this problem, in fact you are more likely to have algal problems. The reason for this is many owners are not actually aware of what a salt water chlorinator does. The mesh cell on your chlorinator is specially coated with rare metals. This coating when electrically charged causes a reaction that releases chlorine and Sodium Hydroxide into the water and produces a Calcium residue on the cell.. This calcium is the white build up you have to clean off regularly. The cell releases the Chlorine ions into the water. When the chlorine passes through the water it increases the pH. As a result if you do not add acid regularly your pool can quickly become susceptible to algae. What should I do? If your pool is green the first thing you should do is check the chemical levels. In 90% of cases the pH will be high. Should I add chlorine? Yes, but remember chlorine increases the pH and unless you add acid as well the algae will continue to flourish no matter how high the chlorine level is. The simplest and cheapest method of removing algae from a pool is acid and chlorine. What if my pool goes cloudy? This can easily happen when you have bombed a pool with chlorine and acid. Often it just means you need to add more acid, but check your pH first. If the pool is still cloudy there are a number of ways to clear it up, depending on what type of filter you have. Diatomaceous Earth filters need regular cleaning but are very efficient and will clear your pool quickly, while sand filters may need a filter aid or ‘blue block’ to assist them. Should I backwash my filter or clean my cartridges? Definitely. D.E. and cartridge filters can filter algae but they clog quickly and until the pool is clean will require regular backwashing or cleaning. Algae burrows through the sand in sand filters making them ineffective so they will definitely need backwashing. Often once the algae is dead you will find the pool needs vacuuming. Make sure the pool cleaner is removed and if you do have to vacuum do it to ‘waste’ or down the drain so you are removing the algae from the pool without clogging your filter. If you have persistent problems or even if you do manage to kill the algae it is a good idea to have your water tested at a pool shop.
If you have a re-occurring problem with algae, look at adding an algaecide to help prevent it’s growth. If you are getting regular green or yellow algae on the pool walls, this is due to lack of chlorine, adding stabiliser will help your pool retain chlorine better.
In recent years we have noticed the re-occurrence of a new (or rather old) form of algae. This algae is one of the oldest forms of life and tends to occur in pools with leaf problems. It is a luminous green colour and will get greener with small doses of chlorine. The reason is that as a defence mechanism the algae will breed when attacked. If you give it a small dose of chlorine one algal spore can breed to 20,000. If the green just won’t go away then this is probably what you are experiencing. To fix this add a copper algaecide to the pool (winteriser or similiar – 40gm/L copper) and bring the pH down into the lower end of the ideal range. Disconnect any automatic pool cleaners. Add one significant dose of chlorine (15L+ of liquid or 1.5-2kg of powder) and run the filter as long as possible. We have found it tends to occur in pools with sand filters which are not as fine as diatomaceous earth or cartridge filters. This is why you should use a filter aid, such as alum or a floc cube, and run them for longer hours. Continue filtering the pool as long as possible daily until the green disappears. Keep the chlorine level at 1ppm (ideal) and do not let it drop until the green disappears. After a few days you will probably need to add chlorine daily; 1 cup good quality powder or 1 litre liquid. The pool will go blue all of a sudden, in some cases the pool will be clean too. It may take hours, days or weeks. You may need to manually vacuum the pool to waste when the water clears if there is a large amount of dirt (dead algae).