Phosphates are the single most under-tested parameter in South Florida pools. Municipal water and well water in Palm Beach and Broward counties run unusually high in phosphates — and high phosphates feed algae faster than chlorine can kill it.
What phosphates are (and why they end up in your pool)
Orthophosphates are a natural nutrient. They show up in pool water from a handful of sources:
- Municipal water (South Florida utilities add phosphate as a corrosion inhibitor — it's not dangerous, but it's present)
- Well water — extremely high in some Palm Beach County areas
- Fertilizer runoff (lawn treatments next to the pool)
- Tree debris, leaves, pollen
- Swimmer sweat, sunscreen, body products
What phosphate level is safe
| Phosphate level (ppb) | Risk |
|---|---|
| Under 100 ppb | Ideal — algae starved |
| 100–500 ppb | Acceptable with normal chlorine |
| 500–1,000 ppb | Elevated — treat next service |
| 1,000+ ppb | Algae bloom likely without aggressive action |
| 3,000+ ppb | You almost certainly already have algae |
Why chlorine alone can't keep up
Chlorine kills algae cells. Phosphates feed new ones. In a phosphate-heavy pool, you're in a chemical arms race where algae grows as fast as chlorine kills it. You'll see: water that turns green within a week of being clear, constant chlorine demand, short-lived “shock” effects.
How we treat it
- Test quarterly (included in our weekly chemistry service).
- If above 500 ppb, dose a lanthanum-based phosphate remover.
- Wait 24–48 hours — phosphate precipitates into the filter.
- Clean or backwash the filter to remove the captured phosphate.
- Re-test.
Myths to ignore
- “Phosphate removers are a scam.” Not in South Florida. Pools north of the Mason-Dixon can sometimes get away without. Ours can't.
- “Just use more chlorine.” You'll lose the arms race and wreck your CYA levels trying.
- “Only test phosphate if I have algae.” By then you've already paid for green-pool recovery that quarterly testing would have prevented.
If your pool keeps going green despite good chlorine, phosphates are the first thing we test. Book a chemistry diagnostic.
Frequently Asked Questions
Ideally under 500 ppb (parts per billion). Over 1,000 ppb, algae grows even with good chlorine.
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