Green algae blooms are the ultimate result of chemical imbalance in pool water, primarily caused by the simultaneous fulfillment of two conditions:
(1). Disinfection ineffectiveness: This is the root cause. When free residual chlorine is insufficient (below 0.5 mg/L) or the pH value is imbalanced (above 7.2-7.8), chlorine's bactericidal and algae-killing abilities will significantly decrease or even become ineffective. When the pH value is frequently below 7.0, disinfectants evaporate too quickly, resulting in a prolonged period where bacteria and algae proliferate due to the lack of residual chlorine.
(2). Eutrophication: Swimmers' sweat, skin flakes, rainwater-introduced spores, and fallen leaves are rich in nitrogen and phosphorus, providing "nutrients" for algae.
Hypochlorous acid (HOCl) and hypochlorite (OCl-) will exist in different ratios under different pH conditions.The percentage of free available chlorine varies at different pH values, as shown below:
|
pH value
|
Effective activity of free available chlorine
|
|
4.0
|
100.0%
|
|
7.0
|
75.0%
|
|
7.5
|
48.0%
|
|
8.0
|
22.0%
|
|
11.0
|
0.03%
|
|
12.0
|
0.01%
|