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.
Stabilised Chlorine
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!
Calcium Hypochlorite - an off white chlorine granules
or tablet. (also known as Shock Chlorine)
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 2 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).
Bromination
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 :
