What's happening to my chlorine?!?

[Double6]

Please help me!! I have a new 20k gallon salt pool (built 11/07). A month ago, it was dicovered my Pentair chlorine generator was defective and it was replaced. All LED lights indicate the new one is working properly. I have had my water tested AT LEAST weekly at Leslie's Pools and each time, I show absolutely 0 FAC and TAC. I've tried superchlorinating by running the pumps for 24 hours at 100% output. No change! I just shocked the pool this morning with 3 lbs Chlor-Brite (sodium dichloride). About 2 hours after I shocked it, I showed about 3 ppm FAC. Now, 12 hours later, it's all gone (0 chlorine!). I run the pumps a minimum of 10 hours a day from 8a-6p. I add 1 qt Muriatic acid about every 3-5 days and 2 1/2 capfulls Pool Perfect with Phos-free once a week. At my last test (this morning), I showed pH at 7.8, TA at 100, Calcium Hardness at 275, CYA at 90, Phosphates were at 100 ppb and the salt level was 3900. I had the techs test for nitrates this time and I showed 0. My water is chrystal clear, never had algae, but what is happening to my chlorine? Any suggestions?
Thanks!
Jeff

 

[Nasty90]

Hello,
Your pool's SWG should be reading salt levels of 3200-3400ppm. What is the control knob set on the box?

 

[Double6]

I'm sorry. I'm not sure what you're referring to. If you're talking about the output level, I have it set to 80%.

 

[Guest]

Have you checked your cell for scale buildup?

 

[Double6]

Yes...there is none. I checked it and cleaned all the filters prior to the superchlorination.

 

[Guest]

Run the generator and then turn it off. Loosen the cell and collect some water from the cell directly(turn everything off first). Test the water for chlorine. It should be high. If it isn't the unit is not working and you should call for service.
If it's generating chlorine then you have something in your pool that is consuming your chlorine.
Are you testing the water yourself or having it tested? What is the chlorine test being used? The DPD test, which is the most common, can bleachout at high chlorine levels.
Just for fun get a cheap 2 way liquid tester that uses OTO (turns shades of yellow) and test your chlorine in the pool. IF it stays colorless you have none. Get the unit serviced.
IF it turns yellow you are generating chlorine.
IF it turns orange to brown you have way too much chlorine and the DPD test that leslies is doing is bleaching out. Turn your output down.
This is why we recommend FAS-DPD chlorine testing in this forum.

 

[Double6]

I'll try that...Thank!
I'm using test strips to monitor the levels myself but, at least once a week, I take a sample to my local pool store and they check it for me.

 

[Guest]

The OTO test, while not that precise, is bulletproof. If there is chlorine it will turn yellow. Strips can bleach out and if they get wet they might not change color at all. Not dependable. Get yourself a good test kit and do your own testing. You want a kit that uses the FAS-DPD chlorine test. For salt level use Aquachek salt test strips.

 

[Poolsean]

Double,

Have you treated your pool for algae lately?

 

[Double6]

I use Phos Free to keep down my phosphate level. Other than that, I've never had an algae problem.