and safety of your swimming pool and spa bath depends to a great
extent on the correct additions of chemicals to the water. Below
are the calculators to allow you to rapidly work out how much
of each chemical to add to water of known volume. See also:
This should be your starting point, if
you don't know how much water there is, it is impossible to calculate
the correct additions.
This calculator will tell you whether your
water is likely to corrode your pool or cause cloudy water and
INDIVIDUAL PRODUCT CALCULATORS
Please click on a link below.
Predissolve dry materials and predilute liquids before distributing
around the pool. Allow sufficient time for thorough mixing before
What about pH? Unfortunately, there
is no easy way to calculate additions for this as there are so
many variables. Our best advice would be to ensure that you have
the total alkalinity level correct. If it is too high, above 200
p.p.m, then the water will be excessively buffered and it will
be difficult to adjust the pH. If it is too low, less than about
80 p.p.m., then there may be large fluctuations in pH for small
additions of correction chemicals. With the total alkalinity about
100 to 140 p.p.m. predissolve small quantities of pH INCREASE
or pH DECREASE and distribute around the pool. Allow up to 12
hours with pumps running to fully mix and then retest.
This is a measure of the alkaline nature
of the water, which at the pH encountered in swimming pools is
predominently bicarbonate. As with most things to do with pool
chemistry there is a compromise situation between corrosion, scaling,
sanitiser efficiency and ease of maintaining pH. The range to
aim for is 80 to 150 p.p.m.
Note: Trichlor will lower total alkalinity
Calcium Hypochlorite will raise total alkalinity
Dichlor will have least effect on total alkalinity.
To raise total alkalinity add TOTAL ALKALINITY INCREASE.
To lower total alkalinity add pH DECREASE or fresh water
A Bromine tablet weighs about 18 gms. As
these slowly dissolve the free bromine level will rise as indicated
by this calculator In spa baths and small domestic pools,
maintain a free bromine level of 2 to 3 p.p.m. In larger more
heavily used pools, or commercial pools where the bather load
is higher, aim for 4 to 6 p.p.m.
These are unstabilised Chlorine granules,
also known as "Shock Chlorine". As a routine sanitiser,
Calcium Hypochlorite is usually preferred for indoor pools where
the effects of sunlight are less. When used outdoors, a separate
stabiliser must be added to slow chlorine loss in sunlight. For
sanitising, the typical free chlorine level would be 2 to 3 p.p.m.for
domestic pools, 3 to 5 p.p.m for heavier used pools. 10 p.p.m
or more is the shock treatment level, following which, the level
should be allowed to drop below 5 p.p.m before bathers enter the
TIP - Add shock chlorine at night so that it can work in
the dark to maintain its strength for longer.
TIP - In soft water, Calcium Hypochlorite also builds the
Calcium content of the water.
NOTE - At free chlorine levels above 10 p.p.m, the water
sample colour using Phenol Red test tablets may be bleached. This
could give the impression there is no chlorine when there is quite
Dichlor is an abbreviation of the chemical
name Sodium Dichloroisocyanurate Dihydrate. (UK Approved Supply
List - troclosene sodium dihydrate) It is also referred to as
Stabilised Chlorine Granules. It provides an easy way to add chlorine
to outdoor domestic pools where the stabiliser resists the chlorine
loss caused by sunlight. The typical free chlorine level would
be 2 to 3 p.p.m. Dichlor is not ideally suitable for "shocking"
or "Superchlorination" For this purpose we recommend
Trichlor is an abbreviation of the chemical
name Trichloroisocyanuric Acid (UK Approved Supply List - trichloro-1,3,5-triazinetrion).
It is supplied in slow dissolving tablets of 200gm for most pools
or 20gm for use in small pools and spa baths. It provides a very
easy way to add chlorine to outdoor domestic pools where the stabiliser
resists the chlorine loss caused by sunlight. The typical free
chlorine level would be 2 to 3 p.p.m. Not suitable for "shocking"
or "Superchlorination". For this purpose we recommend
Calcium Hypochlorite. This calculator
shows the grammes of tablet used for each p.p.m free chlorine.
The principal water hardness salts are
Calcium Carbonate and Magnesium Carbonate. Usually tests for hardness
express the result as mg/litre (parts per million) all as Calcium
Carbonate. If there is too little in your water then calcium salts
from concrete, tile grout and other metals in the pool structure
will dissolve in it. Soft water is therefore corrosive. Too much
on the other hand will form scale. Generally the water should
be kept at around 150 p.p.m as Calcium Carbonate unless your pool
supplier recommends otherwise based on how it is constructed.
If your test shows additions should be made, use Hardness Increase
as as indicated by this calculator.
Where unstabilised forms of chlorine such
as Sodium or Calcium Hypochlorite are used outdoors, it is necessary
to add a separate stabiliser to slow the rate of chlorine loss.
For free chlorine levels above 2p.p.m., aim to achieve a level
of 50-100.p.p.m. Too much however can cause a condition known
as "chlorine lock" when the free chlorine is inhibited
in its action as a sanitiser. In this case it should be lowered
by dilution with fresh water.
A copper based algicide used throughout
the summer to suppress the growth of algae into the pool. Shock
treat the pool with Calcium Hypochlorite
and then maintain a residual copper content at 0.4 to 0.5 p.p.m.
A premium copper based long life algicide
used to suppress the growth of algae into the pool. Shock treat
the pool with Calcium Hypochlorite and
then maintain a residual copper content at 0.4 to 0.5 p.p.m.
This measures a suitable dose of positively
charged polymeric material which which will assist the negatively
charged particles which cause haze to agglomerate together and
be more easily removed by filtration.
For more information on using this product,
first see our Use and Safety
Page. This calculator is used if you are adding 20mg/litre.
Softens water and prevents scaling and
staining of spa baths by chelating the hard water salts present.
A typical dose rate would be 100gm per 1000 litres
An alternative shock to chlorine based
materials, allowing bathers to return to the water sooner. Oxygen
Shock is particularly recommended for use with Bromine tablets.
Dissolve the required amount in 50 to 100gm quantities in water.
Distribute evenly around the water area.
Pool Dose Rate: 300gm per 25,000litres
Spa Bath Dose Rate: 30gm per 1000 litres
QUATKLEAR - Non Copper
A low foam, polyquaternary algicide used
to suppress the growth of algae into the pool. This is a copper
free material. Shock treat the pool with Calcium
Hypochlorite and then use as indicated by the calculator.
This products inhibits the precipitation
of hard water salts which can cause scale and cloudy water.
A blended threshold chelate and low foam
polyquat sanitiser to inhibit the precipitation of hard water
salts and to provide a broad spectrum sanitiser for over winter
conditions. Use at the rate of 3 litres per 25,000 litres. If
algae are a particular problem, then Poolklear Algicide may additionally
be added, although it should be noted that if scale exists on
pool surfaces some copper staining may occur.
A white silicone emulsion to control foam
in spa baths. Used weekly or as required at the rate of 50ml per
1000litres. For an initial dose, use twice the regular dose shown
by this calculator.