Why does pool water turn green, and how do you prevent it?

This is the problem pool owners meet most often, and it is usually tackled from the wrong end: more chlorine goes into the water. Sometimes it works; more often it does not. Because green water is not a cause, it is a result.

First, know this: chlorine alone is not enough

Clarity comes from balance, not from disinfectant alone. When pH drifts out of range, chlorine largely loses its effect. Adding more chlorine at that point does not solve the problem; it only raises the cost and the hardness of the water. The first thing to do when the water turns is not to add chlorine but to measure pH.

Cause 1: The balance has drifted

This is the most common cause. When pH rises, chlorine becomes bound and does no work. Every chemical added without measuring is added in the dark. That is what regular maintenance means: weekly measurement and small corrections are both cheaper and more effective than monthly interventions.

Cause 2: Filtration is not running enough

The whole body of water has to pass through the filter within a set period. If the system was undersized, or the pump is run only a few hours a day to save electricity, the water does not circulate enough. In hot weather and heavy use those hours must be extended; a pool gets dirty as it is used, not as it sits.

Cause 3: Dead zones

Corners where the water does not move, the space under ladders and the base of steps are where algae starts first. Aiming the return jets correctly and not neglecting brushing solves most of this. A robot cleaner will do the floor but will not take the base of the walls as well as a brush.

Cause 4: An external load

A downpour, wind-blown dust and pollen, leaves from nearby trees, a large group swimming at once — all of these load the water. After an event like that, maintenance has to be stepped up; the normal routine is not enough.

What to do once it has turned

Measure first, then act. Shock chlorination carried out before the balance is corrected is usually money wasted. If the green is advanced, staged treatment is generally cheaper than draining the pool; but if algae has taken hold on the shell surface, mechanical cleaning is essential.

The lasting fix is maintenance

A treatment system is absolutely required, but even a correctly specified system still needs its maintenance done on schedule. On the pools we hand over, maintenance and chemical support continue; we also maintain existing pools.