Quick Reference
- What they are: Orthophosphate (PO₄³⁻) compounds that act as algae nutrients
- Common sources: Fill water, fertilizers, cleaning products, organic debris
- Testing units: Usually ppb (parts per billion) or mg/L as phosphate
- When to consider removal: After sanitization is optimized, if recurring algae issues persist
- Key point: Phosphate removers don't kill algae—they reduce algae's food supply
Table of Contents
What Are Phosphates?
In pool terminology, "phosphates" typically refers to orthophosphate (PO₄³⁻) compounds dissolved in your pool water. These are forms of phosphorus, a major nutrient that can accelerate algae growth in aquatic environments.
The EPA identifies excess nutrients—primarily nitrogen and phosphorus—as drivers of "excessive algal growth" in natural water systems. While pool water chemistry differs significantly from natural environments, the basic mechanism is similar: phosphates serve as "algae food," providing nutrients algae need to multiply rapidly when conditions are right. However, in pools, sanitizer management remains the dominant factor in algae control.
The Phosphate Controversy
The pool industry has two distinct camps when it comes to phosphate management:
Camp A: "Stop Chasing Ghosts"
This perspective, popular in DIY pool communities (TroubleFreePool, Swim University), argues that if your chlorine management is solid, phosphates are rarely the limiting factor. The reasoning: proper sanitization kills algae faster than it can grow, regardless of available nutrients. Many pool owners remove phosphates without seeing significant improvements in water quality.
Camp B: "Remove Fuel, Widen the Margin"
Pool industry manufacturers and some professionals recommend phosphate removal to reduce algae's nutrient supply. They argue that lower phosphate levels provide a wider margin for error when sanitation temporarily slips during heat waves, storms, or periods of heavy pool use.
The Balanced View
Both camps have merit. Phosphates aren't usually the root cause of algae problems—inadequate sanitation is. However, high phosphate levels can reduce your margin for error when sanitation slips, potentially making algae blooms more likely or more persistent.
Where Phosphates Come From
Understanding phosphate sources helps explain why some pools struggle with consistently high levels:
| Source | Details |
|---|---|
| Fill Water | Many water utilities add orthophosphate for corrosion control in distribution systems |
| Landscaping | Fertilizer runoff, soil, and organic debris blown into the pool |
| Pool Chemicals | Some metal stain preventers and tile cleaners contain phosphates |
| Detergents | Residual detergents from swimwear, pool toys, or cleaning products |
| Organic Matter | Decomposing leaves, algae, and other organic debris |
Testing for Phosphates
Most pool "phosphate" tests measure orthophosphate (reactive phosphate), not every form of phosphorus. These tests typically use colorimetric methods that develop a blue color proportional to orthophosphate concentration.
Common Testing Units
- ppb (parts per billion) - Most common in pool testing
- mg/L as PO₄³⁻ - Laboratory standard
- mg/L as P - Sometimes used in water treatment
Unit Conversion: 1 mg/L = 1 ppm = 1000 ppb (when expressed as the same compound)
Testing Considerations
- Chlorine can interfere with colorimetric phosphate tests
- Some test kits include chlorine neutralizers (sodium thiosulfate)
- Follow timing instructions carefully for accurate color development
- Test in good lighting conditions for proper color comparison
Professional Testing Supplies
Browse our selection of pool test kits for phosphate testing supplies from trusted manufacturers.
When Phosphate Removal Makes Sense
Consider phosphate removal only after verifying that pool basics are solid:
Prerequisites (Fix These First)
- Free chlorine levels appropriate for your stabilizer (CYA) level
- Consistent sanitization - not chronically under-chlorinating
- Proper filtration and circulation
- Regular brushing and maintenance
Good Candidates for Phosphate Removal
- Pools with recurring algae despite proper sanitization
- High phosphate inputs (landscaping runoff, frequent organic debris)
- Pools in challenging environments (heavy tree cover, agricultural areas)
- Seasonal spikes during pollen or fertilizer seasons
How Phosphate Removers Work
Mechanism
Phosphate removers work by chemically binding with dissolved phosphates to form insoluble particles (flocculation). These particles are then captured by your pool's filtration system.
Many popular phosphate removers are based on lanthanum chloride, which reacts with phosphates to create a precipitate that your filter can remove.
What to Expect During Treatment
- Water cloudiness - Normal as the precipitate forms
- Increased filter loading - Clean or backwash more frequently
- 24-48 hour clearing time - Keep the pump running continuously
- Possible multiple treatments - For very high phosphate levels
- No swimming during cloudiness - Wait until water clears completely
Professional Phosphate Removers
Browse our selection of phosphate removers from trusted manufacturers for effective phosphate control.
Safety and Handling
While treated pool water is safe for swimming once the remover has been filtered out, the concentrate requires careful handling:
Safety Precautions
- Wear gloves and eye protection - Products can be highly acidic (pH 2-5)
- Avoid skin and eye contact - Can cause significant irritation; treat as an acid
- Store away from children - Keep in original containers
- Don't pour directly - Add slowly with circulation running
- Ventilate area - Avoid breathing vapors
- Follow label and SDS instructions - Each product has specific handling requirements
Frequently Asked Questions
Do I need phosphate removal for salt water pools?
The same principles apply. Salt chlorine generators still rely on maintaining proper free chlorine levels. Phosphate removal might help if you're experiencing algae issues despite proper sanitization, but it's not automatically necessary for salt pools.
Why won't my phosphates go to zero?
Zero phosphates isn't necessary or always achievable. Your fill water may contain phosphates, and small amounts will continuously enter from environmental sources. Focus on levels below 125-500 ppb rather than absolute zero.
My water turned cloudy after adding phosphate remover—is this normal?
Yes, cloudiness is expected as the remover binds with phosphates to form particles your filter can capture. Keep the pump running 24/7 until clear, clean your filter more frequently during treatment, and don't swim until the water is completely clear.
Can I use phosphate remover as a preventive treatment?
While some pool owners use phosphate removers seasonally, it's more cost-effective to focus on consistent sanitization and address phosphates only when testing indicates elevated levels or when experiencing algae issues.
Are phosphates dangerous for swimmers?
No, phosphates themselves aren't toxic to swimmers at levels typically found in pools. The concern is that they can make algae control more challenging, and algae can create unsafe swimming conditions.