Swimming Pool & Spa Construction & Maintenance/Chlorine Lock


Jeff C wrote at 2008-05-18 01:49:08
Before assuming "chlorine lock," or anything involving chemical levels, measurements need to be taken of what is in the water.  Specifically, draining water would only be needed if the cyanuric acid (organic chlorine stabilizer) level is above 80 ppm.

The Pool Guy wrote at 2008-05-30 01:50:40
Never heard of your stabilizer causing a chlorine lock.  Cyanuric acid is supposed to keep the chlorine from escaping.  Usually if you cannot hold chlorine there is nitrates or phosphates in the water.  Nitrates and phosphates are caused from fertilizers, bird droppings, leaves, and dirt.  These nitrates lock up the water and a regular shock will not cure it.  The only way to break a chlorine lock is to shock it 10 times the amount than you normally would.  Usually a liquid shock is recommended because it is cheaper and does the job faster.  For your size pool I would recommend putting in 3 five gallon tubs of liquid chlorine and letting it run for 24 hours.  You will either get a very high reading of chlorine or you will set back your chlorine reading to 0 on total chlorine and zero on free chlorine.

aquaezy wrote at 2014-11-03 01:16:20
Hi Vinney

Chlorine lock? has nothing to do with sTabilised chlorines.  Recent research has shown that stabiliser levls can exceed 400 ppm and it will actually enhance the condition of the pool water.  A more likely cause of your problem is a high level of chlorine, high TDS (Total Disolved Solids) or a condition called Chlorine demand which is the result of a combination of phosphates.  Get your pool shop to do a full water test including Phosphate levels and TDS.  Dilution is the remeedy for high TDS while phosphetes need to be treated.

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Deb Carney


Filter questions, chemical questions, problems with water, leaks, pool pump problems any problem you may have with your pool chemistry, filter, pump.


Pool and filter repair for 15 years. Very experienced in the chemistry of water.

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