Taylor Technologies•Featured Sponsor
Taylor K-2006 Complete DPD-FAS Pool Test Kit
Lab-grade titration kit for accurate Free Chlorine, Total Alkalinity, Calcium & Cyanuric Acid.
How to Fix Pool Chlorine Lock (Why 10ppm Chlorine Won't Kill Algae)
You test your pool and the kit turns deep yellow indicating 8 to 10 ppm of Free Chlorine. Yet the water is cloudy green, algae is dividing across the walls, and the local pool store says you need to buy $150 of extra shock.
You are suffering from Chlorine Lock (hyper-cyanuric saturation). Cyanuric acid acts as sunscreen for chlorine, but when CYA climbs past 80–100 ppm, it forms an unbreakable chemical cage around chlorine molecules. Only 0.5% of your chlorine remains active as hypochlorous acid (HOCl).
0MS CYA DRAIN CALCULATOR
Chlorine Lock Dilution & Drain Calculator
Enter your pool volume and tested Cyanuric Acid level to calculate the exact percentage of water to drain and refill to reset your pool back to the 40 ppm safe zone.
WATER TO DRAIN
60% Drain
9,000 GallonsTARGET CYA POST-REFILL
40 ppm
Restores active HOClMINIMUM SHOCK LEVEL
16 ppm FC
Based on CYA ratioCHEMICAL COST WASTED
$180/mo
Pucks & shock in locked waterADVERTISEMENTSponsored
01Stop Using All 3-Inch Trichlor Pucks Immediately
Every single 8 oz 3-inch trichlor tablet you dissolve adds 3.3 ppm of Cyanuric Acid to your pool water. If you burn 3 pucks per week in summer, you add over 40 ppm of CYA every month. Switch immediately to unstabilized liquid chlorine (12.5% sodium hypochlorite) or Cal-Hypo.
02Execute a Partial Drain and Refill (The Only Real Cure)
There is no magic chemical powder that removes cyanuric acid safely. Commercial 'CYA remover' enzymes cost $80 per bag and fail 90% of the time. The only physical remedy is to drain the calculated volume of high-CYA water with a submersible pump and refill with fresh municipal tap water (which has 0 ppm CYA).
03The 7.5% Rule: Match Free Chlorine to New CYA
Once your water tests at 40 ppm CYA, keep Free Chlorine between 3.0 and 5.0 ppm. At this concentration, 1.5% of chlorine remains freely unbound as hypochlorous acid (HOCl) — more than enough to eradicate algae spores and oxidize bacteria within 60 seconds of contact.
ADVERTISEMENTSponsored
Ready to Balance pH, Alkalinity & Chlorine?
Don't battle green water with random chemicals. Use our 0ms dynamic water balance engine to calculate exact chemical additions for your entire pool volume and maintain crystal clarity.
Launch 0ms Recipe Converter ➔Free Instant Tool • No Signup Required