Phosphates
Phosphates are nutrients present in pool water that can promote algae growth when free chlorine is inadequate.
Definition
Phosphates are nutrients present in pool water that can promote algae growth when free chlorine is inadequate.
Typical Values: Target: below 500 ppb; treat with phosphate remover if above 1,000 ppb and algae is recurring
In Plain Language
Phosphates (orthophosphates and polyphosphates) enter pools from fertiliser runoff, leaves, dust, some municipal water supplies, and certain pool products. They act as a nutrient source for algae. Some pool chemistry systems (particularly in commercial applications) use phosphate removers to reduce algae potential. However, most pool chemistry authorities note that adequate free chlorine is far more important for algae control than phosphate removal.
Why It Matters
High phosphate levels can make algae harder to control, but fixing low free chlorine is always the primary intervention.
Typical Values
Target: below 500 ppb; treat with phosphate remover if above 1,000 ppb and algae is recurring
Last reviewed: 2026-06-01