High Chlorine Level

[Woodland Creature]

Please forgive me but I am an amatuer and homeowner with a 20' x 40' inground pool in the NY area. I've taken my water to be tested at a reliable pool store and for 10 years I have successfully kept the pool properly balanced. Since I have a heater this is watched very carefully. For the past two weeks I've been getting high free chlorine readings in the pool. All other readings are normal. I've tested at the store and myself. Following the store's recommendation I shut down the chlorinator down for a few days then ran at a very low level. They also had me dechlorinate with chemical treatment. None of that worked. After that I tried filling the pool, which was at a lower level water than usual, with hose water. I realize the tap water has chlorine but in the past this has dropped normal levels to low. It's also rained a bit. The water still reads high chlorine - more purple on AquaChek than the highest level. The funny thing is the water does not smell like chlorine. And we have never had high chlorine in ten years. We've always had normal or low chlorine (which was easily corrected with the pool store recommendations). I guess I'm looking for reasons why this is sustained so long. Is my neighbor dumping chlorine at nght? I'm joking. I have great neighbors. But I can't figure it out and the pool store is scratching theri heads. Any throughts?

[LegsOnEarth]

What kind of chlorinator is it? If it's an errosion feeder and you just dailed it down to zero, it may still be feeding chlorine anyway (especially if it's 10 years old and hasn't had any parts replaced on it). I would probably start there.

Otherwise, what are your complete water readings?

[waterbear]

What is your CYA (stabilizer, cyanuric acid) level? I suspect that it is very high and that would explain why the chlorine is not dissapating Also, the higher the CYA the higher you NEED the chlorine for the same amount of sanitizing activity. Please post a full set of test results (not done with strips) so we might better know what is happening in your pool. If you have a chlorinator I assume it is a trichlor tablet feeder. Trichlor adds 6 ppm cyanuric acid for every 10 ppm of free chlorine added. The chlorine gets used up and the CYA builds up over time. Once it gets very high the chlorine does not dissapte as fast (nor is it as active against algae and microbes in the water).

Is your chlorinator by any chance a Hayward CL-200? These are known to clog and be stuck either all the way closed or open no matter where the dial is set. This could also be the explanation for the high chlorine levels. If the chlorinator is the problem then replace it with a Pentair Rainbow Lifeguard unit model 320. It is a much better design that works well.

It would be helpful if you would post numbers for test results and not just say readings are normal. It tells us nothing about what might be happening and there really is not such thing as a 'normal' reading. There are pools where 'normal; chlorine is 1-2 ppm and pools where 'normal' chloruine could be as high as 15 ppm (depending on how low or high the cyanuric acid is).

If your pool store can't figure this one out I would look for another pool store. Or better yet, get yourself a Taylor K-2006 test kit (not the K-2005) and start testing your own water with the precision you need to balance it yourself!