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Swimming pool Problems / Cause / Solutions

It is very difficult to make one definite diagnosis when faced with symptoms of swimming pool problems about the water. You should use all the evidence when considering what to do (e.g. test results) and go with the one you think is most likely.

swimming pool problems

The water’s pH is a measure of its total acid-alkalinity balance — the relative proportion of acids and alkalis in the water. Simply put, water that is either too acidic or too alkaline will cause undesirable chemical reactions.

If the water is too acidic, it will corrode metal equipment, cause etching on the surface materials, and cause skin irritation. If the water is too alkaline, it can cause scaling on the pool surface, and plumbing equipment, and can cloud the water. Additionally, both high acidity, and high alkalinity alters the effectiveness of the chlorine. The chlorine won’t destroy pathogens as well, if the water is too alkaline, and it will dissipate much more quickly if the water is too acidic. On the pH scale, zero indicates extreme acidity, 14 indicates extreme alkalinity, and 7 indicates a neutral state. The recommended pH-range for a swimming pool is between 7.2 and 7.8.

To raise or lower pH, acids or alkalis need to be added to the water. For example, adding sodium carbonate (soda ash) or sodium bicarbonate (baking soda) will generally raise the pH, and adding hydrochloric acid (approx. 30% solution) or sodium bisulphate will lower the pH.

Maintaining the proper balance of chemicals in the pool is a continual process, because any new element (oils from a swimmer’s body, a shot of chlorine, stuff that falls in the water) changes the chemical composition of the water.

If the pH is too high, or not high enough, pool cleaning can take much longer than normal. Once the chemicals that make up the chlorine have cleaned the pool water, their residuals either combine with another chemical, such as ammonia, or are broken down into single atoms which render the chlorine harmless. Sunlight speeds these processes up – that is why, particularly in warm climates, it is necessary to add chlorine to the pool more frequently than in other, cooler places. In addition to pH, the following levels should also be checked: total alkalinity, calcium hardness, and total dissolved solids.

While the bacteria-killing properties of chlorine are very useful, chlorine also has some side effects, that can be annoying to humans, and possibly even hazardous. Chlorine has a very distinctive smell that most find unpleasant, and some find overwhelming. There is also the “itch factor” — chlorine can cause certain skin types to become itchy, and irritated. The hypochlorite ion contained in chlorine can also cause many fabrics to fade quickly when not rinsed off immediately after exiting the pool.

Is pH Really That Important?

The pH is one of the most important factors in pool water balance, and it should be tested and adjusted on a weekly basis. pH is the measure of how acid/ alkaline the swimming pool water is.   A pH of 7.0 is neutral – below 7.0 is acidic, above 7.0 is alkaline. It should be kept within the range of 7.2-7.8.

What happens when the pool is too acidic?
(pH is low):

1.  If your swimming pool is Marbelite or plaster, the pool water will begin to dissolve the surface, creating a roughness
which is ideal for pool algae growth. A similar result occurs in the grouting of tiled swimming pools.

2.  Metals corrode – and this includes swimming pool equipment, pipe fittings, pump connections, etc. As the swimming pool walls, and metal parts corrode, sulphates are formed. These sulphates are released from the water onto the walls, and floor of the
swimming pool causing ugly brown and black stains.

3.  Chlorine, which is used as a disinfectant in the swimming pool water, is activated and lost to the atmosphere very quickly.  The water is not being sanitised, and we are throwing away our money by adding chlorine when the pH is too low.

4.  When we swim, our eyes and nose burn. Our swimwear fades, and perishes. Our skin gets dry and itchy.

What happens when the pool is too alkaline?
(pH is high):

1.  The calcium in the swimming pool water combines with carbonates and forms scale, just like in our kettles. This calcification is seen  most at the waterline, where it traps dust and dirt, turning black with time.

2.  The swimming pool water starts to become cloudy or murky and it loses its sparkle.  Catch yourself buying clarifier frequently?  This could be the result of your pH being too high.

3.  The calcium carbonate has a tendency to plate out on the sand in the swimming pool filter, effectively turning it into cement.  So your filter becomes a cement filter, and loses its ability to trap dirt and other debris from the pool water.

4.  As the pH rises, the power of the chlorine to act on foreign particles is lost. At a pH of 8.0 the pool can only use 20% of the chlorine you put in. So 80% of it goes to waste and you would need  5 times as much chlorine to provide the disinfection you need.

Swimming pool maintenance
The five keys to maintaining water quality in your swimming pool include:

  • Filtration
  • Chlorination
  • pH level
  • Total alkalinity (TA)
  • Calcium hardness.

The water in your pool is pumped through a filter to remove debris and particles. How long you need to run the filter depends on the size of your swimming pool, and the horsepower of your pool pump. If you are unsure, check your instruction manual or consult with a pool maintenance company. Remember, that even when you are filtering your pool according to specifications, about 35 per cent of the water still won’t be filtered.

Chlorine is a chemical that disinfects the water and helps to remove debris. You should use a chlorine stabiliser to extend the chlorine’s half-life. Generally, the longer your filtration cycle, the less chlorine you will need. Similarly, the more chlorine you use, the shorter your required filtration cycle. Remember that your chlorine requirements will be affected by a range of factors, including your pump and filter system, water temperature, water level, amount of debris, and the number of swimmers in your pool.

pH level
The pH level indicates how acidic or alkaline the water is at any given time. A pH level of 7 means that water is neutral; above 7 means the water is alkaline, while below 7 indicates acidity. You should aim for a pH level of between 7 and 7.6. If the water pH is higher than 8, anyone who swims in the pool is at risk of skin rashes, while a pH of lower than 7 can sting the swimmers’ eyes. Some of the many factors that can affect your pool’s pH level include heavy rain, lots of swimmers, and pool chemicals. Remember to regularly check your pool’s pH level.

Total alkalinity (TA) 
Total alkalinity (TA) means the sum of all alkaline chemicals in your water. If TA is too low, the pH balance can become unstable; concrete and painted pool surfaces will also deteriorate over time. TA and pH are interconnected; for example, raising the TA could also raise the pH. Make sure you don’t disrupt your pool’s pH when adjusting the TA, and vice versa.

Calcium hardness
Calcium hardness refers to the amount of the mineral calcium dissolved in your water. Low calcium levels will deteriorate pool surfaces, while high calcium levels will leave a ‘scum’ or scale on surfaces and equipment.

General water quality suggestions
Be guided by pool professionals, but general suggestions on maintaining good water quality in your swimming pool include:

  • Check your pH and chlorine levels daily. Preferably, these tests should be done before the first swim of the day, to make sure the water quality hasn’t altered overnight.
  • In very hot weather, it is a good idea to check the pH, and chlorine twice daily.
  • Remember that heated pools need more chlorine than non-heated pools.
  • Brush, and vacuum your pool on a regular basis.
  • Regularly check the pump, skimmer boxes, and other pool equipment, and repair or replace parts as necessary.

Water Treatment Troubleshooter


Possible Cause

Possible Reason



Cloudy Water

Build up of dirt & bather pollution. Insufficient chlorine or poor filtration Backwash filter then super chlorinate. Add
clarifier to polish water.
Liquid Chlorine


Start of algae growth Insufficient levels of chlorine. Super chlorinate. After 24 hours Liquid Chlorine
backwash filter. Maintain chlorine level above 3ppm. Prevent recurrence of algae growth.
Liquid Chlorine
Chlorine Granule
Chlorine Tablets


Chlorine ineffective Over stabilization Dilute pool water and super chlorinate. Liquid Chlorine


Ineffective filtration Filter blocked or filter media needs renewing Check sand, filter cartridge or D.E. Media See below


Suspended particles Precipitation of salts due to high PH or high alkalinity. Correct pH and/or alkalinity Dry acid

Unpleasant Water

High combined chlorines. Free chlorine levels too low Dilute pool water  

Sore eyes/throat.
Itching Skin

Detergents from cleaning compounds getting into pool water. Reaction between chlorine
and detergent.
Use chlorine compatible cleaners. Tile & liner cleaner


Water too acidic or alkaline. pH too low or too high. Correct pH as in chart. Dry Alkali or Dry Acid

Chlorine level difficult to maintain

Sunlight destroys chlorine. Chlorine not stabilized. Use stabilizer or stabilized chlorine. Stabilizer. Chlorine granules or Chlorine tablets.


Build up of pollutants Insufficient chlorination. Super chlorinate Liquid Chlorine


High water temperature Organisms multiply more rapidly. Increase dose rate of sanitiser. Chlorine granules or chlorine tablets.

Apparent inability to get a chlorine reading on test kit in spite of chlorine addition.

Chlorine levels may be too high High chlorine content bleaches reagent in test tablet Dechlorinate. Allow chlorine to reduce naturally over a period of time. If very high reduce with chemicals. Neutraliser

pH too low

Low pH of local mains water Insufficient Dry Alkali being added. Add Dry Alkali as per instructions. pH to be between 7.2 & 7.6. Dry Alkali


Use of acidic chlorine donors.      

pH too high

High pH of local mains water Insufficient Dry Acid being added, or applied incorrectly Add acid as per instructions .Maintain pH to be between . 7.2 & 7.6. Dry Acid


Use of alkaline donors. High alkalinity Reduce alkalinity to 200ppm Check pH Dry Acid


Salts being leached from new concrete pools Self correcting over a period of time Add acid to maintain pH between 7.2 & 7.6. Dry Acid

pH levels erratic

Insufficient bicarbonate to buffer pH. Low total alkalinity. Add bicarbonate. Min 100ppm required. Alkalinity Increaser

pH locked

Too high a level of bicarbonates. Topping up from the mains water can increase alkalinity in hard water areas. Reduce alkalinity to 200ppm Check pH. Dry Acid

Low Alkalinity

Bicarbonates reduced by dilution particularly in soft water areas. Mains water has low level of bicarbonates. Add bicarbonate. Min 100ppm required. Alkalinity Increaser

Pool walls feel slimy

Algae growing Insufficient chlorination and pool wall brushing. Super chlorinate to kill algae. Sweep or vacuum debris. Prevent recurrence with algaecide. Liquid Chlorine Algaecide

Dirt on pool wall at water line.

Build up of body fat, sun oil or cosmetics. Irregular cleaning of surfaces. Clean with environment friendly chemical. Tile & Liner Cleaner

Rough scale formed on pool surfaces.

Water out of balance Ratio of calcium hardness to total alkalinity incorrect Check levels of pH, alkalinity and calcium. Seek advice from 1st Direct. Go to ‘Contact page

Sharp edges round tiles.

Grout being leached by water. Mains water too soft. Regrout the pool. Increase calcium levels to min. 250ppm & maintain. Consider changing sanitiser to HTH Calcium Hypochlorite which will ensure calcium levels are maintained. HTH Calcium Hypochlorit

Ineffective Filtration

Sand filter
Is the sand level correct?


no: No Not enough sand to filter out particles. Renew or top up sand. Go to ‘Contact page


yes: Blocked filter or filtration needs assistance Backwash filter and use filter aid. Sparkle


Cartridge filter:
Is cartridge in good clean condition?


no: Filter allowing particles to pass through. Renew cartridge Go to ‘Contact page


yes: Filter requires assistance Backwash and use filter aid. Sparkle

Pool left unattended for long period of time

Unable to treat daily. Use Fi-Buoy. Remember to run filter daily on a timeclock.   Fi-Buoy

PPM – The number of “parts” by weight of a substance per million parts of water

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

Diagnosis (1)

Dirt or bather pollution in water suggesting inadequate filtration

Cure (1)

Backwash the filter, and raise free chlorine levels to around 10 parts per million using unstabilised chlorine. Polish water by adding a clarifier.

Diagnosis (2)

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.

Cure (2)

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 unstabilised chlorine.

Diagnosis (3)

The filter is ineffective or has become blocked.

Cure (3)

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.

Diagnosis (4)

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.

Cure (4)

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.

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