Chlorine Lock

  • Last Post 07 June 2022
tessaduncan posted this 05 June 2022

Pool store water test 4 days ago indicated chlorine lock (FC=0, TC=4ppm, CYA=10ppm, all others in range). Added 4lbs oxyshock per their advice to 25k gal inground vinyl pool.  Water is clear. Been testing daily (strips) and chlorine always reads zero. Shouldn't I have gotten at least a low Cl reading if lock was broken?  Do I add chlorine?  Haven't added any since oxyshcok treatment. Thx

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JCMC70 posted this 07 June 2022


You don't have chlorine lock. You just don't have any chlorine. That's because you don't have enough stabilizer (CYA) in the water. CYA interacts with chlorine to prevent the sunlight from "eating " all the chlorine. Without the proper amount of CYA you could add 5 gallons of chlorine to the water and it would be gone in a matter of hours.

The bare minimum CYA level in a vinyl lined pool is 30ppm. The ideal level is 40ppm. For a 25000 gal pool you would need to add 6 pounds of dry stabilizer or 2 gallons of liquid stabilizer to raise the CYA level to 40ppm.

If you use liquid stabilizer you can slowly pour it in front of a return jet, with the pump running, and let the pump run for 48hrs. If you use dry stabilizer you will need to put it into a sock or knee high nylon stocking (that works fastest), tie the sock/stocking to a pole, like a pool pole, and hang it in front of a return outlet with the pump running. Squeeze the sock/nylon every few hours to help disburse the stabilizer and run the pump continuously until all of the stabilizer has been dissolved and for 48hrs after that.

And if you will allow me, please get rid of the test strips. They are worthless. Get a good reagent test kit like the Taylor K2006 and test the water yourself. Not only will you get a more accurate reading but you will avoid bad advice from a pool store employee who sold your shock that you didn't need instead of stabilizer that you do need.


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tessaduncan posted this 07 June 2022

Just added a sock of stabilizer and will run for at least 48 hours.  Thank you for your advice.

JCMC70 posted this 07 June 2022

You're welcome.