Once the pool is correctly balanced it needs to be sanitised to kill bacteria, algae and germs. This can be done with chlorine (liquid, granular, tablet or salt) bromine, ozone, ionic and bizanide.
hlorine is the most popular in one form or another followed by bromine, ozone and ionic. Chlorine is also the most cost effective and most readily available.
Chlorine is an oxidizer. It combines with oxygen to decompose things much the same as rust and fire. Rust is very slow, fire is quick to burn through wood taking minutes however chlorine oxidizes in fractions of a second once it contacts organic material such as bacteria, algae, perspiration. Larger organics such as insects, leaves, dirt will take days and demand high levels of chlorine so it is best to remove these. The more organic material the longer it takes with a minimum of 30 minutes recommended at the appropriate chlorine levels.
How well the chlorine works is dependent upon the quantity of chlorine in the pool and the pH of the pool water. If the chlorine level is too low it will get used up before it can do its job. If the pH is either too low or too high the chlorine becomes ineffective, no mater how much chlorine is added it will do little to nothing for the bacteria, algae and germs.
The ideal pH range for chlorine is between 7.2 and 7.6 with an acceptable range of 6.8 to 7.8.
When chlorine is added to water it changes into one of 2 compounds, hypochlorous acid or hypochlorite ions. Hypochlorous acid is a very effective sanitiser while hypochlorite ion is a very poor sanitiser. The pH of the water determines which compound the chlorine changes into. The higher the pH, the more hypochlorite ions formed i.e. at a pH of 8.5, 90% of all chlorine added becomes hypochlorite ion. At a pH of 6.0 a large amount of hypochlorous acid is being formed but at this pH the majority is going straight into the atmosphere and not sanitising your pool.
When looking after your pool, the two most important things are pH and sanitiser level. With chlorine it is important to know the “Free Chlorine” level/reading. This is the amount of chlorine in the water that is able to oxidize the bacteria, algae and other organic matter. Once the bacteria and organics have been oxidized the chlorine is either destroyed or changes form. If there is too much organic matter in the pool, particularly urine and perspiration the chlorine will change form and combine with these organics to create chloramines (combined chlorine).
Chlorine smell – is caused by chloramine compounds. Contrary to popular belief, it’s too little chlorine that causes the smell, not too much. Too little chlorine permits chloramine compounds to form. It is these compounds that have the strong smell affecting the eyes, nose and skin.
The combined chlorine level can be determined by testing the pool for Free Chlorine and total chlorine.
Total chlorine – Free Chlorine = Combined chlorine.
Combined chlorine levels should be as low as possible (less than 0.2 ppm) if not chlorine levels will need to be increased or a super chlorination (10 ppm free chlorine) may be required.
Enviro Pool Sticks also oxidize organics without adding any chemicals to the water considerably reducing the chlorine consumption, formation of chloramine compounds and pool care required.
The following types of chlorine are commonly used in swimming pools, although there are other types, these are the main ingredients.
Liquid Chlorine/Sodium Hypochlorite
Liquid chlorine is very easy to use, with no pre-mixing required. It is more commonly available in 5, 10, 25 or 200 litre containers at a strength of 12.5% available chlorine. It has a limited shelf life and should not be stored for more than a few weeks or purchased from suppliers who have a low stock turnover. It has a high pH of around 11-12 and as such will raise the pool pH. It is also unstabilised and so will loose strength rapidly. (Refer to chlorine stabiliser in following section.)
Calcium Hypochlorite/Cal Hypo
This is the most common and cheapest form of chlorine. It is a white granular or powder product containing 65% available chlorine. When added to water it quickly goes into solution but does not dissolve completely leaving a calcium residue. If mixed in a bucket this calcium residue can be discarded rather than added to the pool where it will fall to the bottom and add to the calcium hardness of the pool. It has a high pH of 11.7 is unstabilised (refer to chlorine stabiliser in following section) and must be stored in a sealed container away from moisture, oils, petrol and other chemicals. If stored properly it will last for months.
This is a stabilised chlorine where the stabiliser (cyanuric acid) has been added as opposed to sodium Hypochlorite and Cal Hypo. It is available in tablets or sticks containing 90% available chlorine. This product has a long shelf life, dissolves completely. It has a pH of 2.8 so will lower the pool pH and total alkalinity.
This is a stabilised granular chlorine (refer to chlorine stabiliser in next section) with 63% available chlorine. Drichlor is easy to dissolve and has a long shelf life. The pH is also more neutral between 5.5 and 7.0. This will have little effect on pool pH and alkalinity.
All forms of straight chlorine rapidly dissipate in the presence of sunlight. In other words if the pool chlorine is unstabilised, free chlorine will be lost from the pool at a rate of up to 30% per hour in sunlight i.e. if the pool has 1 ppm or 100% at 9 am in the morning, by 10 am it will have 70%, by 11 am it will have 49% and by the afternoon there will be very little left and this does not allow for any used to oxidise bacteria and other organic material.
Stabilised chlorine or pools with stabilizer added stop this loss and maintains the free chlorine a lot longer. Stabiliser, pool conditioner, sunscreen etc are the common names used for cyanuric acid. On its own it is a white granular product that dissolves very slowly (2-5 days). It can be added to the pool in a number of ways.
- premixed in a bucket of water and slowly added through the skimmer box so it dissolves in the filter (do not backflush filter for 5 days).
- Broadcast over the water surface and allowed to settle on the pool floor (do not vacuum pool for 3-5 days).
- Add to a floating dispenser. Cyanuric acid does dissolve quicker in warm water.
While stabiliser slows down the loss of chlorine, the reaction of free chlorine with cyanuric acid produces a form of combined chlorine (chlorimide) which has reduced effectiveness hence the higher free chlorine level required in stabilised pools. The Chlorimide is still active enough though to show up as free chlorine residual when tested.
Although most pool test kits cannot test for Cyanuric acid proper stabilisation requires 30-50 ppm with a maximum of 60 ppm. Levels above 100 ppm will cause the chlorine to become ineffective and cloudy water. It is best to have too little than too much.
Stabiliser is a residual product in pool water and is only reduced by filter backwashing, rainfall, pool top up and splashing water out of the pool. Without these it should last 3-4 months.
Another method of sanitising and chlorinating pools is to use salt/sodium chloride. When salt water passes through an electrolytic/electrolysis cell or salt water chlorinator the sodium gets separated from the chlorine. The chlorine then changes into one of 2 compounds, hypochlorous acid or hypochlorite ion depending upon the pH of the water. (Refer to chlorine in previous section). The remainder of the process is the same as using chlorine.
With salt chlorination it is important to maintain lower calcium levels to prevent calcium build up on the electrolytic cell/chlorine generator obstructing its operation. It is also important to maintain salt levels in the pool to avoid damage to the chlorine generator.
Salt water chlorinators are manufactured by a large number of suppliers, some are self cleaning, others not. They are all designed to operate with dissolved salt concentrations between 1800 – 6000 ppm (0.18 – 0.6%) with an average of 3000 – 5000 ppm. This is a lot less than sea water which has salt levels of 35,000 ppm.
Chlorine stabiliser can be used in salt water pools just as it can be in normal chlorine pools. If the chlorine levels get too low during usage it is best to use other forms of chlorine to lift levels straight away rather than having to wait several hours for the salt chlorinator.
The salt in the pool is only used up slowly by the salt water chlorinator and therefore only needs to be added to the pool 1-2 times/month. An Enviro Pool Stick is also recommended to considerably reduce the salt requirement even further, helping maintain a more balanced pool with much lower maintenance and running costs.
An important distinction of salt water pools over chlorine pools is they lack chloramines/combined chlorine. Chloramines cause the strong smell effecting the eyes, nose and skin. The process of generating chlorine also burns off chloramines.
Bromine is used extensively as a sanitiser in spas, hot tubs, indoor pools, fountains and water features. It is chemically very similar to chlorine. Bromine reacts more slowly than chlorine so is a lot less subject to dissipation in sunlight. Like chlorine, bromine when added to water forms one of two compounds; hypobromous acid or hypobromite iron. Hypobromous acid is a very effective sanitiser while hypobromite iron is very ineffective. Like chlorine the pH determines which compound is formed although unlike chlorine hypobromous acid will be formed within a large pH range of 5.5 to 8.0.
The most commonly used bromine contains 28% chlorine. This has the advantage of burning off any hypobromite ions and helping to oxidize other organic particles. This combination product usually comes in tablet form for floating dispensers.
When bromine comes into contact with organic compounds such as urine and perspiration it forms Bromomines rather than Chloramines. These bromomines give off very littler odour have low eye irritation and are still very active sanitisers. All of the above reasons make bromine an excellent sanitizer in spas and hot tubs.
Bromine residual should be maintained between 2 and 4 ppm and is measured using the DPD # 1 test used to measure free chlorine. If your pool test kit does not include a bromine scale then bromine residual is approximately 2.25 times the reading on the chlorine scale.
Ozone is a natural molecule found in the upper atmosphere. It is also a natural sanitizer that can be manufactured/generated on site where it is required. Once generated it is injected straight into the water. Ozone is a very active product lasting only a few minutes in the water after injection. No residual remains in the water so the pool water needs to be constantly treated or chlorine needs to be used to maintain a residual.
Ozone generators are specialised equipment and best set up by those specialised in this field.
Ozone pools (like any other pool) also greatly benefit from an Enviro Pool Stick helping oxidize any organic matter in the pool reducing the necessity to use chlorine.
Ionic sanitisation is the use of ions and minerals such as copper and silver or magnesium and potassium to oxidize or kill bacteria, algae and other organic matter. Some of these ions and minerals have been used for centuries in treating drinking water and controlling disease and infection.
There are two main types or systems.
- Those using a combination of cooper and silver.
- Those using a combination of magnesium and potassium.
Copper and Silver – use in water sources is well documented. Copper is known to kill algae and provide an environment unsuitable for it to live while silver is known as bactericide. The system works by passing a low voltage DC (direct current) electrical current between two copper and silver electrodes installed in the filtration pipework. This produces low levels of cooper and silver in the water thereby killing the bacteria and algae. It is important to maintain a pH between 7.0 and 7.4 and balance the pool as required for chlorine and salt water pools.
The copper and silver electrodes/anodes are sacrificial (get used up) and do require replacing on average every 2 years. The pool water only needs to be tested every week to ensure correct levels of ions, pH and alkalinity.
An oxidiser such as Enviro Pool Stick, hydrogen peroxide, potassium mono-persulphate or chlorine is required from time to time to polish the water free of oils like suntan lotion, body fats, hair oils, perspiration, etc. The Enviro Pool Stick is best suited to this as it adds no chemicals or products to the pool, instead using the sun’s energy to oxidise the organic matter, further reducing the running costs and maintenance leaving a more stable, balanced pool.
Copper is also an essential element for humans. It is estimated that adult requirements are about 2.3 mg per person per day.
Magnesium and Potassium
A blend of magnesium chloride and potassium chloride is used to sanitise the pool. Potassium chloride is converted the same as sodium chloride in salt water pools releasing chlorine to provide a residual oxidizer. The combination of these irons is likened to mineral pools used around the world, particularly New Zealand for the relief of aches and pains and general healing of the body.
The process of combining these minerals also produces magnesium hydroxide (caustic soda) which stays in the water and raises the pH. This may not affect the process though.
Bags of mineral blend need to be added as required to maintain the nominated concentration (ppm). This may only be needed every few months depending upon rainfall, backwashing and pool usage, etc.
Magnesium is also an essential element required by humans for normal growth with a daily intake recommended.
Algae are tiny plants or seaweed that multiply and grow in swimming pools if nutrients are present and the level of chlorine or sanitizer is low or not maintained. They can multiply at a staggering rate from 1 spore to millions in hours.
There are 3 main types of Algae found in pools: Green, Mustard and Black.
Green Algae; is the most common algae found floating in swimming pools or coating pool surfaces. If untreated they will quickly turn the pool green.
Mustard Algea: has a greeny beige appearance and settles on pool walls causing a slimy yellow film.
Black Algea: appears in clumps attached to tile grout, corners, steps and pool surfaces. This algae grows into the grout and produces a wax providing an outer covering to protect itself and making it almost impossible to penetrate with chemicals and kill.
Solutions and Removal
- Green Algae is the easiest to treat and remove. It can even be flocculated (adding a chemical to the surface of the pool) dropping all the suspended organic matter to the floor of the pool where it can be vacuumed to waste saving many hours/days of filtering and treatment.
- Green algae is usually treated by super chlorination with 10-20ppm chlorine in the evening. Brush down and clean the walls and floor of the pool and run the filtration non-stop until the water clears maintaining the chlorine above 3ppm. An algaecide can also be used to kill the algae and will also help prevent the return after super chlorination.
- Mustard algae is much more resistant to chemical treatment and clings more tightly to the pool walls than green algae. A specialised algaecide is best added in the morning to treat this algae. Walls and infected areas will then need to be vigorously brushed and vacuumed to waste. Filters can not remove this algae.
- Black Algae is very difficult to treat and get rid of once it is in the pool. Spot treatments can be done using specialised algaecides and brushing with a stiff brush or stainless steel wire brush (being careful not to damage the pool surface) trichlor tablets can also be rubbed on areas to spot treat. In worst case scenarios the pool may need to be partially drained and cleaned.
With all algae’s it is best to avoid the problem in the first place by maintaining the required water quality and frequent cleaning of the pool floor and walls.
Algaecides are residual chemicals lasting between a week and six months.