Green, cloudy or milky water: maintenance issue or equipment fault

Start with a test, not a guess

The colour of the water is a symptom, not a diagnosis. Before anyone adds chemicals or replaces equipment, test the water.

The US Centers for Disease Control and Prevention (CDC) calls chlorine and pH the first defence against germs. It recommends a pH of 7.0 to 7.8 and a free chlorine level of at least 1 ppm in pools, or at least 2 ppm where cyanuric acid (stabiliser) is used. It advises testing chlorine and pH at least twice a day, more often when the pool is busy, and says a DPD test kit is more accurate than test strips. In the UAE, follow the ranges your local authority sets, which may differ.

If you cannot see the floor of the pool clearly, keep people out of the water until it clears.

Green water

Green water almost always means algae. AstralPool, the pool equipment brand of Fluidra, lists the usual reasons:

• Low chlorine. When free chlorine drops too low, algae grow.
• High pH. Above about 8.0, chlorine loses much of its strength. AstralPool links water that is green but clear to a pH above 7.8, even when chlorine is present, and notes that salt chlorinators tend to push pH up.
• Sunlight and low stabiliser. Ultraviolet light breaks down chlorine. Stabiliser protects it.
• Too little circulation or filtration time. Chemicals need moving water to reach every part of the pool.
• A filter problem. A clogged or faulty filter lets algae thrive.

Hayward, the pool equipment maker, adds that algae can arrive with wind, rain or contaminated equipment.

Cloudy water

Hayward lists several common causes of cloudiness:

• Poor water balance. Imbalanced pH, alkalinity or calcium hardness can cloud the water. High pH causes scaling and cloudiness.
• Insufficient filtration and circulation. Clogged or dirty filters leave particles in the water, and poor circulation stops chemicals and filtration reaching every area.
• Inadequate sanitation. Low chlorine, often after heavy use, high temperatures or under dosing, lets bacteria and algae grow.
• Environmental load. Heavy rain, wind blown debris, dust and organic matter.

Milky water

Milky usually describes heavy, white or grey cloudiness. The causes overlap with ordinary cloudy water: balance, filtration and sanitation. One cause is easy to miss. Pentair's filter manual lists air bubbles coming out of the return jets with the pump running as a sign that air is entering the system, from a low water level, a clogged skimmer basket, a leak in the pump lid or a leak in the suction line. Fine bubbles can make water look milky and are a sign of a fault, not a chemistry problem.

Maintenance issue or equipment fault

The US Department of Energy's guide on pool pumps takes a clear position: most water clarity problems come from improper chemical maintenance rather than from debris hanging in the water. It adds that filtration and circulation do matter when the system is not run long or fast enough for the chemical feeder or generator to work properly.

That gives a sensible order of work.

Likely a maintenance issue if

• the test shows low chlorine, high pH or poor balance
• the problem followed heavy use, a party, rain or a dust storm
• the water improves within a day or two once chemistry is corrected and the filter is cleaned

Likely an equipment fault if

• chemistry has been correct for several days and the water still will not clear
• the filter pressure stays high after cleaning, or the gauge does not return to zero when the system is off
• the pressure drops while the baskets are clean, which Pentair says can mean a clogged impeller or an obstruction in the suction line
• air bubbles come out of the returns
• the pump runs for fewer hours than set, or the timer or controller has failed
• the chlorinator or dosing pump is not delivering

What a specialist will check

A pump and filter specialist will usually:

1. Retest the water and check stabiliser and calcium levels.
2. Inspect the filter media, laterals or cartridges for damage, channelling or wear.
3. Check the pump's flow, run time and programming.
4. Look for air leaks on the suction side.
5. Test the chlorinator or dosing equipment.

Restoring clear water

AstralPool's recovery sequence for a green pool is a useful outline: test, correct pH, shock with a strong chlorine dose (sometimes twice), clean the filter, brush and vacuum, then run the filtration until the water is clear, which can take several days. Retest and keep monitoring afterwards.

If you have followed those steps and the water is still green, cloudy or milky, stop adding chemicals and call a specialist. More product rarely fixes a mechanical fault.