Why Does Pool Water Turn Green and How Is It Fixed?
Pool water turns green when free chlorine levels drop and algae growth begins. This is usually caused by irregular chlorination, insufficient filtration runtime, or unbalanced pH. The fix is shock chlorination, an algaecide treatment, and running the filter continuously until the water clears.
Root Causes of Green Water
The most common causes include several days without chlorination, insufficient filter runtime, chlorine becoming ineffective due to high pH, and increased organic load after heavy bather use. Metal-rich source water (copper, iron) can also contribute to a green-brown discoloration.
Step-by-Step Correction Process
First, pH is brought into the 7.2–7.4 range, then a shock dose of 3–5 times the normal chlorine level is applied. Combined with an algaecide, the filter should run continuously for 24 hours while the pool floor is vacuumed. Daily chlorine and pH checks continue until the water clears, usually within 24–48 hours.