What causes green pool water?
Green water means algae. Algae blooms when one or more of these conditions exist: chlorine levels drop below effective range, phosphate levels are high (algae food), circulation is poor or filter isn't running enough, or the pool hasn't been brushed, allowing algae to anchor on surfaces.
North Shore pools are especially prone to algae in July and August when humidity is high and rain introduces phosphates and contaminants. Coastal towns like Beverly and Salem see even more humidity-related issues.
Step-by-step: clearing a green pool
1. Test your water — pH, chlorine, phosphates, CYA
2. Adjust pH to 7.2–7.4 (shock works better at lower pH)
3. Brush all walls, floor, and steps thoroughly
4. Triple-shock the pool (3 lbs per 10,000 gallons)
5. Run the filter 24/7 until water clears
6. Backwash or clean filter every 8–12 hours
7. Test and treat phosphates once water clears
8. Rebalance all chemistry once clear
When to call a professional
If the water is dark green or black-green, if you can't see the bottom, or if shocking twice hasn't made a visible difference — it's time to call in a CPO-certified technician. Persistent green water usually means an underlying chemistry imbalance that store-bought test strips won't catch.
We use professional Taylor test kits and photometer analysis to identify the exact issue — whether it's high phosphates, over-stabilized water (CYA lock), or a filtration problem. If your filter isn't performing, we offer pool filter repair to restore proper flow and water clarity. Learn more about our water chemistry service.
Pool still green after trying everything?
We'll diagnose the root cause and fix it. Serving Peabody, Danvers, Beverly, Salem & the North Shore.
Call (978) 882-5932