If the green pool water is caused by an Algae Bloom – IT IS UNSAFE FOR SWIMMING.
There are 3 causes of green pool water:
1. Lack of Chlorine.
Without chlorine, your pool water will quickly start to grow algae and turn to a green pool water. It should be noted that water with an algae bloom can be a breeding ground for mosquitoes and other insects, but more importantly it is unsafe to swim in.
2. Oxidized Metals
Oxidized metals, usually copper will also turn your pool water green. Metals can be introduced through acidic source water, cheap algaecides or from metal components in pool equipment (most notably copper heater elements). Shocking your pool oxidizes these metals, and if they are present in high enough quantities they will turn pool water green. If left untreated, high amounts of metals may stain your pool’s finish and turn a swimmer’s hair green.
3. Excessive Pollen in the Air
Airborne pollen is too small for your sand filter to remove. As it builds up in the water and settles it gives the water a green or yellow look. Despite its unattractive look, green pool water caused by pollen generally has no ill health effects.
As a rule of thumb, we always recommend that you avoid swimming in green pool water. In most situations you can rectify the problem yourself with the right chemical and attention, however there are situations when you may need to empty your pool and start fresh with clean water.