There are four main causes, and your test kit or pool professional can help pinpoint which applies to your pool.

1. Fine Suspended Particles (Milky White Water)

Often caused by dissolved hardness salts precipitating due to high pH, high alkalinity, or both.

How to fix it:

Lower pH or total alkalinity using dry acid.

To correct pH: add 1 lb of dry acid per 10,000 gallons per day until levels normalize.

To correct alkalinity: double the dosage.

Add acid gradually, and correct alkalinity first, since dry acid lowers both.

Important: Always follow the manufacturer’s instructions on all pool chemicals.

2. Dirt and Bather Waste (Low Chlorine or Poor Filtration)

Insufficient chlorine or inadequate filtration allows debris and contaminants to build up.

How to fix it:

Backwash the filter.

Superchlorinate to 10 ppm using unstabilized chlorine (sodium hypochlorite or calcium hypochlorite).

Add a clarifier to polish the water.

3. Over-Stabilization (High Cyanuric Acid Levels)

Using stabilized chlorine can lead to excessive stabilizer (CYA), reducing chlorine effectiveness and causing haze.

How to fix it:

Drain or perform an extra-large backwash to replace some water with fresh water (reduces CYA).

Superchlorinate to 10 ppm afterward.

4. Blocked or Ineffective Filter

Sand may be degraded, coated with calcium, or simply past its useful life.

How to fix it:

Check the filter sand and replace if needed.

If sand is intact but coated with calcium (common in hard water areas), treat with a filter cleanser to restore filtration performance.

Contact a pool professional if you are not comfortable replacing sand yourself.

At some stage, chlorine levels have fallen, or chlorine has become ineffective, allowing algae to form in the water.

Shock (superchlorinate) with an unstabilized chlorine such as calcium hypochlorite or sodium hypochlorite, or use an algeacide. Shock dosing usually produces the fastest results. For greenish discolorations (where the water is no more than tinted green), superchlorinate to 10ppm. For more serious problems, where the water is pea-soup green and the bottom is not visible, shock in a 2 stage dose 6 hours apart. This will kill the algae.

Brush off any algae that may remain on pool surfaces. Look for growth behind steps or ladders and around underwater lighting.

Backwash the filter or clean cartridge 24 hours after treatment to remove dead algae from the filter media.

Thereafter maintain chlorine at around 3ppm to prevent a recurrence.

A regular treatment program of an algaecide or a chlorine with added algaecide is recommended for all pools. Consult your pool professional for the best treatment for your pool.

There are three possible causes - your test kit or pool professional can help you to see which is the most probable.

1. pH problem - the water could be too acidic or too alkaline. The pH of the human eye is around 7.4-7.5 - anything higher or lower will irritate. Correct the pH. To lower the pH, add dry acid at a rate of 1 pound per 10,000 gallons per day until correct reading is obtained. To raise pH, dose at the same rate with soda ash.

2. High combined chlorine - chloramines are known to be an irritant. Note carefully the results you get on your DPD no3 test. Also, if you get an unpleasant chlorine smell, its odds on that the problem is due to high chloramines. Break the chloramines down by super chlorinating the pool. Aim to allow no more than one third of the total chlorine to be in the form of combined chlorine.

3. Incompatible Detergent - some detergents used for cleaning pool sides and removing scum lines are incompatible with chlorine. The resulting reactions in the water can lead to eye and skin irritation. Similar reactions can occur if soaps or shampoos get into the water. Super chlorinate to clear out the detergents. Change to cleaners that are chlorine compatible or abandon their use. Ask your pool professional for advise on these chemicals. Have phosphate levels checked for your pool, as this could cause other problems with water balance.

High levels of copper in the pool. This can arise either because of over-use of copper based algaecides, or because the pH of the pool water has been allowed to drop to a point at which it starts to corrode the copper in your pool equipment. Correct the pH.

Treat your pool with a metal removing chemical. Ask your pool professional for advise on choosing this product.

These are the two most likely causes.

1. The chlorine level in the pool is so high that it bleaches the coloring agent in the test kit. Determine the approximate level of chlorine by diluting the sample of pool water with an equal quantity of natural or distilled water; multiply the answer by 2. If there is still no reading, repeat the process and multiply the answer by 4...and so on. If the actual chlorine reading is not too high (i.e. around 10ppm), suspend dosing and allow it to drop over a period of time.If the chlorine reading is significantly higher, the chlorine level should be lowered. The best way is through dilution (adding fresh water) of the pool water.

2. High  levels of ammonia in the pool water.

See a pool professional for advice on the treatment of ammonia.

There are three possible causes.

1. The hypochlorous acid (free chlorine) is being decomposed by ultra violet from the sun's rays. For pools using liquid chlorine (sodium hypochlorite) or calcium hypochlorite, add stabilizer (cyanuric acid). This should be dosed directly into the pool, NOT pre-mixed with the chlorine. Alternatively, switch to a stabilized chlorine such as - dichlor granules or trichlor tablets

2. High water temperature. The logic is simple. Micro-organisms are more at home in warm water and breed more quickly. A greater number of organisms will create a greater and higher chlorine demand.

As a rough rule of thumb to bear in mind if there is a heat wave,      if the pool water temperature goes above 80 degrees Fahrenheit, the chlorine demand will double for each increment of 10 degrees. The dose rate of chlorine must be increased proportionately. Keep a close check on chlorine levels in hot weather.

3. Chlorine levels have not been high enough. This causes a build-up of pollutants, and therefore an increase in chlorine demand. Super-chlorinate the pool.

This is usually due either to low pH of water supply (especially in soft water areas) or to the use of acidic chlorine, such as trichlor

1. Correct the pH. To raise the pH, add soda ash as directed per day until correct reading is obtained.

2. Consider changing to a high pH chlorine source. This helps achieve a natural balance between the low pH of the water and the high pH of the chlorine donor. Dichlor is roughly pH neutral; calcium hypochlorite and sodium hypochlorite are high pH chlorine donors.

A persistently high pH is usually caused by one of the following:

High-pH mains (fill) water, which is especially common in hard-water areas.

Use of alkaline chlorine products, such as calcium hypochlorite or sodium hypochlorite, which naturally raise pH.

Hardness salts leaching from new concrete or mosaic pools, which temporarily elevates pH as the surfaces cure.

How to Fix It

The solution is the same for all three causes: lower the pH.

Add dry acid daily as directed until the pH reaches the correct level.

Additional Guidance

For causes #1 and #2, consider switching to a low-pH chlorine source to maintain long-term balance.

Trichlor is the recommended chlorine donor because its naturally low pH helps offset high-pH fill water and high-pH chlorine sources.

For cause #3, the issue is temporary.

As the new concrete or mosaic surface finishes curing, the leaching of hardness salts will reduce, and the pH will stabilize on its own.

The reason will be that the total alkalinity will be too low to buffer the pH

Add sodium bicarbonate to ensure the total alkalinity remains above 100ppm.

The water is over buffered due to high alkalinity. This is a not uncommon problem in hard water areas where the mains feed water has a high total alkalinity.

Add dry acid to lower the total alkalinity to below 200ppm

The local feed water is low in bicarbonates so that whenever the pool is topped up from the mains, it dilutes the bicarbonates in the pool. This is a particular problem in soft water areas.

Add sodium bicarbonate to raise the total alkalinity to around 100ppm.

There are two possible factors at work here:

1. In soft water areas, the grouting is being etched by the pool water. This is because there is insufficient calcium in the water. There is a tendency for water to form an equilibrium by searching for calcium - in this case from the grouting or plaster substrate.Regrout the pool and increase calcium levels in the water by adding calcium chloride  so as to achieve a minimum calcium hardness level of 250ppm. Alternatively, use calcium hypochlorite for shock dosing or for regular sanitization - calcium will be automatically added to the water in using this sanitizer.

High levels of sulphate in the water. You will need to get your pool professional to test for sulphates to confirm this diagnosis.

2. High sulphates caused by

a) high sulphates in the mains water

b) the frequent use of dry acid (sodium bisulphate) or

c) use of aluminum sulphate as a water clarifier.

If you suspect factors (b) or (c), dilute with fresh water and switch to alternative methods of lowering the pH (e.g. Using trichlor as the main pool sanitizer), or clarifying the water (a sulphate-free treatment). There is not much you can do about (a).

The balance between pH, total alkalinity and calcium hardness is incorrect, and the water is technically 'scale forming'.

Test for pH, total alkalinity and calcium hardness and bring them within recommended parameters. It is best to carry out a 'Langelier' water balance calculation (see water balance), or ask your pool professional to do this for you.

This is probably algae forming on the pool surface due to insufficient chlorination at some stage, or to a 'dead spot' in the water circulation.

Sweep the affected areas vigorously to remove as much algae as possible, then shock dose with an unstabilized chlorine (follow the procedure set out for killing algae). Prevent a recurrence by periodic use of an algaecide