Algae or Green Pool?

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).


Cloudy Pool?

Water can go cloudy for two reasons. One is a chemical imbalance and the other is suspended solids.  After super-dosing a pool with chlorine to kill algae it is very common for the pool to go cloudy. This is a combination of both problems. The dead algae will make the pool cloudy and as a result of the excess chlorine the pH will have risen, also affecting clarity. How do we fix it? The first thing to do in all cases is check the pH level of your pool. In most cases the pool just needs acid and by running the filter for a day the pool will return to normal. If this is not the case there are a number of products which can help you. Floc or Alum is thrown in your pool with the pump off. It gathers all the suspended solids and drops it to the bottom. After 24 to 48 hours when the pool is clear you can vacuum this dirt to waste. Those with a sand filter will benefit from the use of a pool blue block. The blue blocks contain clarifiers and other chemicals and when placed in the skimmer basket they help the filter collect more of these particles. The very simplest solution of all is of course just to run the filter continuously until it clears and will save you buying chemicals, however do get your water tested just to make sure everything is chemically balanced.
Disconnect any automatic pool cleaners as these will continually stir up the dirt and will make the pool take longer to clear. If you have a sand filter you may find that when you vacuum the dust from the bottom it returns to the pool. This means the dust is most likely topsoil and is finer than the sand in your filter. This dust may need to be vacuumed to waste. This problem can also occur with the residue from low quality powdered chlorine. This residue can be stirred up by your cleaner and will make the pool water milky white. Disconnecting the cleaner and running the filter will settle this residue to the bottom but it will have to be vacuumed to waste. This is why we recommend you use either low residue american granular chlorine or liquid chlorine. Even though the low residue chlorine may appear expensive you will use significantly less making it much more cost effective.
A correct pH, chlorination and continuous filtration (24Hrs if possible) with the cleaner disconnected should clear any pool within days.
If your pool is still cloudy after 3-4 days check that your filter is working and that the water is still balanced. Inadequate water flow will affect filtration efficiency.

Black Pool?

If your pool water is black then this is an extreme case of algae. A large dose of chlorine and acid will be required. Use less in fibreglass and vinyl pools, as they can stain easily. If you have black spots on the walls then this is another form of algae known as black spot. It is often caused by a high pH (your pool needs acid). It is hard to remove. The pH has to be kept at about 7.0 and the pool broomed regularly for about 2 weeks. An algaecide like Tropiclear or LoChlor will help this process.

In older pools a stain can occur that will turn the floor or walls black in colour. This not an algae – to check run your hand or foot over a section of black. If it is slimy and smooth you have algae, if it is rough and cannot be moved by brush it is a stain. Black staining can occur from excessive copper levels, which is predominant in older marblesheen pools. Whenever a black stain appears add a few litres of acid to the pool to bring the pH back down to just above 7.0. The stain should disappear. If any remains after 24 hours a stain remover for metals will remove the rest.

What is PH?

pH stands for Potential of Hydrogen and is a measure of the acidity of a solution, in our case pool water.

The pH is a measure of the Acid level in a pool. On a scale of 1 to 14 it goes from Acidic (1) to Basic (14). A pH of 7 is for neutral water. The recommended Ph for a swimming pool or spa is 7.2 to 7.6. This is controlled by adding acid to lower the pH or Soda Ash to raise it. Buffer actually raises the alkalinity but as a by-product it will also raise the pH.

Concrete, pebblecrete, marblesheen and concrete pools have a tendency to be too basic and require acid regularly. Fibreglass and vinyl pools will have a tendency to be too acidic and may require soda ash occasionally. This is due to the surface of the pool. For more information see Alkalinity.

An incorrect pH in heated pools or spas can lead to corrosion of heater elements, seriously shortening their life expectancy. This is why we now recommend Nature 2 (pH neutral) instead of Bromine (acidic/corrosive) in spas.

If your pH gets too low, the water becomes acidic and this can result in swimmers getting sore eyes.

If your pH gets too high it allows algal growth and does not let the chlorine sanitise the water properly.

Hydrochloric Acid is the chemical term for the acid used however when in this weaker form it is also called Muriatic acid. Various brands have labelled it as pool acid, ph down and ph decreaser.

What is Alkalinity?

Alkalinity is a measure of the amount of alkaline material in the water, usually present as bicarbonates, pH carbonates and hydroxides. The amount of alkali in the water will determine how easy it is for changes in pH to occur.

The Alkalinity or temporary hardness is what prevents a change in ph (otherwise known as a buffer) in your pool. The recommended level is approximately 100ppm. To raise your alkalinity add Buffer (Sodium Bicarbonate) and to lower it use Soda Ash (Sodium Carbonate). Acid is often used to lower alkalinity but it will not reduce the levels it will just appear to change them due to the method of testing used, but it will lower your pH significantly.

The pH is critical for water balance and by increasing your alkalinity you can buffer the pH in your pool so that it won’t fluctuate as easily. Just remember that when adding Buffer to a swimming pool to increase the alkalinity, it will also increase the pH, so you may need to add more acid.

One of the biggest influence on your pH and Alkalinity is the surface of your pool. Concrete, marblesheen and aggregate pools have a surface high in lime and calcium carbonate. Leaching from this surface will increase both the alkalinity and pH. This is why you will use more acid in a concrete pool. To help prevent this new concrete or pebblecrete pools should be dosed with 4-8kg of buffer when first filled. This will cause the surface to ‘seal’ reducing leaching. In fibreglass, vinyl or painted pools the sealed surface means that there is little influence on the water chemistry. This will result in usually lower pH and Alkalinity level. This is not a problem and is why Buffer is not really required in smooth surface pools.

An important thing to note is that when you adjust your alkalinity you will affect your pH. If you try our free software which uses the Langelier index to balance water you will discover that the alkalinity has a fairly minor impact on water balance in comparison to your pH. With a pH between 7.2 and 7.8 you can have an alkalinity anywhere between 30 and 300 without a problem. Tap water is usually around 30-40 which is why buffer is not regularly required in most pools.


Discoloration of the walls of a swimming pool is due to incorrect water balance.

If the walls are slimy to touch then you have algae. This will need to be killed with a large dose of chlorine. See Algae help for more information.

The other alternative is a stain. Stains are often caused by various minerals or metals falling out of the water due to an incorrect water balance. The first step is to check your water balance. In most cases the pH is the problem. Black copper stains or brown manganese or iron stains both predominantly occur when the pH is high. Reducing the pH in most cases will remove the stain back into solution. If you have problems with re-occurring black stains, get your copper levels tested and do not use algaecides as they contain high levels of copper. This is common in many ioniser based systems as they use Copper/Silver electrodes. This is one reason why ionisers are not sold in every pool shop.

Salt chlorinators, due to the sudden change in pH they create, can often produce brown iron/manganese stains, which will start opposite the return jet. Again, adjusting your pH will solve this problem.

Once the water balance is correct any remaining stains can be corrected using a stain remover or metal remover.

Staining is very common in vinyl and fibreglass pools. Brown dusty stains on the liner are best removed with an organic acid stain remover.

Salt Water

There are two reasons you may have salt water in your pool. Many people have a preference to swimming in salt water and this can be achieved by merely adding up to 10 (25kg ea) bags of salt in a 50,000 pool. The most common reason however is for use with a salt water chlorinator.

Salt is actually Sodium Chloride. Salt Chlorinators work by breaking up the salt molecules and releasing the chlorine into the water. This is how they chlorinate your pool for you. They do require some maintenance but they save the day to day manual dosing.

There is no such thing as too much salt in a pool. While tap water has a very low salt level [0.03-0.15%], many ocean pools, such as those operated by local councils, are successfully treated and chlorinated with levels up to 3.5% or 35 ppt. A salt chlorinator by comparison usually operates on only 0.4-0.7% (4-7ppt) salt.

It is impossible to guess an accurate salt level and while some chlorinators test for salt they can only approximate. The best way to test your salt is to take a water sample to any poolshop, or you can even buy test strips now!! We recommend all salt chlorinators operate at between 0.6%-0.7% salt. This will also help extend the cell life.

Salt levels can be increased by the use of liquid chlorine which is sodium hypochlorite, i.e. contains salt, however it is only a small amount, unless used for extended periods.

See: Salt ChlorinatorsProducts

This PDF factsheet contains seasonal maintenance information for owners of salt chlorinators on concrete pools.

Pool Care Guide for Salt Water Pools [PDF]