The various chemicals can be divided into four groups according to their function.
Sanitiers ~ This group of chemicals is the most important in treating your pool. Their job is to quickly kill any bacteria or viruses that get into the water so that they cannot multiply and cause infections in swimmers. Most of them contain chlorine.
Calcium Hypochlorite - an off white chlorine granules or tablet.
- It contains 65% available chlorine and when dissolved in water it leaves some solids.
- It is slightly alkaline so it will increase the pH.
- It should be dosed into a skimmer or the solution can be added through a small dosing pump.
- 75 grams adds approximately 1 part per million of free chlorine to 10,000 gallons of water.
- The level of free chlorine should be maintained at between 1 and 3 parts per million. This is measured with a chlorine (DPD 1) test kit.
- When used in an outdoor pool the sunlight breaks up some of the free chlorine. So in sunny weather it may be difficult to maintain the correct level of chlorine.
- It is also used as a shock treatment to rid the pool of algae or to burn off unpleasant chlorine by products (chloramines).
- In order to stop chlorine being broken down by sunlight it is combined with a stabiliser - cyanuric acid.
- Cyanuric acid can be added separately or more commonly it is supplied as stabilised chlorine granules or tablets.
- The problem with all stabilised chlorine products is that as well as stopping the sunlight breaking down the chlorine they also make the chlorine less effective. Therefore it is important not to get too much cyanuric acid in the water.
- The cyanuric acid level can be tested with a test kit. The only way of getting rid of cyanuric acid is by dumping water.
- There are two forms of stabilised chlorine
- Stabilised Chlorine Tablets (sodium dichloroisocyanurate) - This is a white tablet which adds chlorine to the water just like any other sanitiser but it also adds stabiliser at the same time. It has a pH close to neutral (7) so that it will have little effect on the pH of the pool water. It is added by dissolving the required quantity in warm water. 60 grams will add 1 part per million chlorine to each 45 cubic metres (10,000 gallons) of pool water.
- Stabilised Chlorine (Trichloro isocyanuric acid) - This is normally supplied as a 200 gram tablet which adds chlorine to the water just like any other sanitiser but it also adds stabiliser at the same time. It is acidic so it will reduce the pH of the pool water making it necessary to add an alkalinity builder to the water to prevent corrosion or the attack of concrete or tile grout. The tablets are slow dissolving. They are usually put in the skimmer to dissolve over several days. One 200 gram tablet will add approximately 4 parts per million of chlorine to each 45 cubic metres (10,000 gallons) of pool water, this might seem a lot in a small pool but remember, it is dissolving slowly
- Hint: Add Chlorine in the evening instead of the morning, as this can halve your chemical costs.
Why? At night, chlorine is used up doing useful work in your pool, like oxidizing all the sweat and sun-tan lotion from your pool party. During the day, it is mostly wasted -- lost to the UV in the sunlight. Depending on stabilizer levels, and sunshine, you can lose half the chlorine in the pool in as little as 30 minutes! Even when your swimming pool is stabilized, you can lose half the sanitizer in 4 hours. But, at night, all of the chlorine used is doing something useful to your pool water!
- Some pools are fitted with circulation feeders called brominators.
- These use a sanitiser called bromo-chloro-dimethyl hydantoin (BCDMH).
- BCDMH is supplied in the form of white tablets which are loaded into the brominator and the pool water is pumped over them.
- BCDMH should not be added directly to the pool or through the skimmers.
- The level of active bromine in the pool is tested with a bromine test kit and the brominator is adjusted to give a bromine level between 2 and 4 ppm. The pH level can be allowed to rise to between 7.8 and 8.0 so very little pH minus is required.
- As the chlorine and bromine in BCDMH are used up the amount of the DMH part of the chemical in the pool increases. Excessive DMH affects the disinfection efficiency so the level must not be allowed to get too high. The concentration should not exceed 200 ppm.
- Apart from the higher free bromine and pH levels all the other pool parameters such as alkalinity and calcium hardness are the same as in chlorinated pools.
pH Correction ~ All chlorine based sanitisers become less effective at killing bacteria and viruses as the pH rises (becomes more alkaline).
- To keep the chlorine working it is recommended that the pH is kept below 7.6.
- However if pool water becomes less alkaline it also gets more corrosive and less comfortable to swim in.
- Also, if pH drops below 7.2 it will start to attack some liners.
- Therefore, the pH is recommended to be above 7.2. So the normal range that a pool water should be kept at is 7.2 to 7.6 (ideally 7.4 to 7.6).
- On most pools the pH will tend to rise so pH minus (sodium bisulphate) is added. The exception to this is if trichloro isocyanuric acid is being used in which case the pH will go down and an alkalinity builder will be required.
- The pH is tested using pH test kit which uses phenol red tablets in a comparitor tube
- It is difficult to predict how much acid will be required to reduce the pH to a precise level as it depends on what else the water contains.
- For instance a soft water will require less acid to adjust the pH than a hard water.
- We suggest adding 500 grams for every 45 cubic metres (10,000 gallons) and then re testing after 12 hours and redosing if necessary. You will soon become familiar with the amount your particular water requires.
- To dose dissolve in warm water in a clean plastic container and distribute evenly around the pool with the filter operating.
Flocculants ~ Substances which improve the efficiency of your sand filter. They release a coagulant to help filter sand remove fine particles which could pass through the filter and make the water cloudy. The most commonly used flocculant is aluminium sulphate.
Granular flocculant (aluminium sulphate)
- Forms a gel on top of your pool filter enabling the filter to remove finer particles. It is very simple to use.
- Backwash the filter. Place 60 grams of aluminium sulphate for each 45 cubic metres (10,000 gallons) of pool water in the skimmer or strainer basket.
- The pool filter should be run continuously for at least 48 hours and only back washed during this time if the pressure rises to the level recommended for backwashing.
- In the event of backwashing repeat dose.
- Aluminium sulphate should not be used with diatomaceous earth or cartridge filters.
Sparkle Water Clarifier Liquid Flocculant (Aliphatic Polyamine)
- Flocculates the fine particles in the water making them stick together in clumps so that they can be filtered out.
- If your pool goes cloudy it can be added directly to the pool to clear overnight.
- It can be used in conjunction with, or instead of, aluminium sulphate.
- To clear cloudy water add 250 mls per 45 cubic metres (10,000 gallons).
- Dilute in a plastic bucket and distribute evenly around the pool with the filter operating.
- For routine use add 60 mls per 45 cubic metres (10,000 gallons) weekly.
Balanced Water ~ Water which is not corrosive and will not scale up your pool heater is said to be balanced.
Alkalinity Builder (Sodium Bicarbonate)
- In areas where the tap water is soft, or if stabilised chlorine tablets (trichloro isocyanuric acid) are used it will be necessary to add alkalinity to the water.
- Adding alkalinity builder will slowly increase the pH of the pool water.
- Water with little alkalinity is corrosive to pool pumps, heat exchangers, concrete and tile grout.
- The alkalinity should be kept above 120 ppm.
- In hard water areas it will already be over this level.
- Alkalinity builder is added direct to the pool.
- It will sink to the bottom but will quickly dissolve if brushed.
- 1 kilogram of alkalinity builder will increase alkalinity by approximately 12 ppm in 45 cubic metres (10,000 gallons) of pool water.
Calcium Builder (Calcium Chloride)
- If you have a tiled pool and are in a soft water area (an area where you kettle doesn’t fur up) it is important that you keep sufficient calcium in the pool water.
- Hard water will naturally contain enough calcium.. If there is insufficient calcium in the water of a tiled pool the water will tend to dissolve the calcium in the grout making it soft. Eventually the grout will disappear leaving sharp edges which can cut the feet of bathers.
- In a tiled pool the calcium hardness should be kept above 200 parts per million.
- The calcium hardness can be increased by adding calcium chloride or by using calcium hypochlorite as your sanitiser.
- Spent calcium hypochlorite ends up as calcium chloride.
Summary of pool water conditions that you should aim for :
||1 - 3mg/l
||2 - 4mg/l|
||7.2 - 7.8
||7.2 - 7.8|
||120 - 150mg/l
||120 - 150mg/l|
||100 - 150mg/l
||100 - 150mg/l (200 tiled pools)|