Swimming Pool Problems – Pool Water Problems
Swimming Pool Problems
It is very difficult to make one definite diagnosis when faced with symptoms of
swimming pool water problems. You should use other evidence when considering
what to do (e.g. test results) and go with the one you think is most likely.
Symptom : Black Spots
These are caused by black algae.
Unfortunately, black algae is very tenacious and will require quite a bit of
effort to remove. For minor problems, try persistant brushing combined with a
good black algaecide. You will also need to clean the filter thoroughly. If
the problem is more major, you may need to drain the pool and chlorine wash.
Symptom : Cloudy / Milky Discolouration
Dirt or bather pollution in water suggesting inadequate filtration
Backwash the filter and raise free chlorine levels to around 10 parts per
million using unstabilised chlorine. Polish water by adding a clarifier.
You are using stabilised chlorines and there is too much stabiliser in the
water. This causes the chlorine to take longer to kill micro-organisms and so
they build up and give a haziness to the water.
Lower levels of stabiliser by replacing some of the water – either by performing
an extra large backwash or by draining to waste. Then top up with fresh mains
water. Superchlorinate by raising free chlorine levels to around 10ppm using
The filter is ineffective or has become blocked.
Check the sand and replace if necessary (or get your dealer to do this.) If the
sand particles have become coated in calcium (this happens mainly in hard water
areas), the filter is not blocked and everything else seems fine, sharpen the
sand with a filter cleanser.
Fine suspended particles in water that are formed as dissolved hardness salts
transform to small solid particles by a process called precipitation. This is
probably a result of a high pH or alkalinity.
Lower the pH using dry acid until an adequate reading is obtained.
Symptom : Cloudy Green
Algae is present in the water. This suggests that chlorine levels have dropped
too low or it has become ineffective.
Shock dose with unstabilised chorine to kill the algae (10ppm for green tints,
25ppm if the bottom of the pool is not visible.) Brush off remaining algae on
pool surface (including underwater lighting and step ladders.) Wait 24 hours.
Backwash filter to clear out dead algae. Use water clarifier to remove haziness.
Maintain chlorine levels at around 3 ppm. Use an algicide (or chlorine with
added algicide) regularly if algae becomes a big problem.
If you are using stabilised chlorine and testing indicates adequate levels of
chlorine but you are still getting algae, see Diagnosis 2 above
Symptom : Rusty red coloured water
Pipes or other steel/iron-containing fittings in the circulation system are
being corroded by a high water acidity (low pH level.) The corroded particles
are then oxidised by chlorine shock doses and this causes rust.
Act quickly to prevent the liner being stained and other damage. Contact your
pool dealer / installer and see whether you can drain down and replace the water
all at once or whether you need to use progressive dilution. Use a good liner
and tile cleaner to remove any rust stains.
Replace the offending metal fittings with PVC or copper. Ensure that the water
has a pH and total alkalinity level within recommended limits.
Symptom : Sore throat, skin irritation and stinging eyes.
The pH level of the water is too high (alkaline) or too low (acidic).
Aim for a pH of around 7.4. Use dry acid to lower the pH or soda ash to raise
High levels of combined chlorine (chloramines). An unpleasant “chlorine” smell
tends to accompany this problem. Perform a DPD no3 test and check the results.
Superchlorinate the pool (up to 10ppm free chlorine) in order to break down the
Ensure that combined chlorine forms no more than 1/3 of the total chlorine in
You are using a detergent that is not chlorine compatible, for example to remove
tide-marks or to clear pool sides. Some detergents react with the chlorine and
these reactions can cause irritation to the skin and eyes. Traces of soaps and
shampoos (from bathers) can cause similar reactions.
Superchlorinate to ensure that all of the detergent(s) has/have reacted away.
Switch to cleaners that are compatible with chlorine or clean manually.
You are using the pool whilst sweaty or wearing makeup. Perspiration and
cosmetics both contain nitrogenous compounds which react with free chlorine.
Have a thorough wash or shower before entering the pool.
Symptom : Tinted or blonde hair turns a green colour after swimming.
Levels of copper in the pool are too high. It may be that the water is too
acidic (low pH) and that this is corroding the fittings of the heater.
Alternatively you may be over-using algicides that are copper-based.
Your local pharmacist should be able to recommend a shampoo to restore the
hair’s original colour
Use copper-based algicides more sparingly. Raise the pH of the water using soda ash.