High chlorine in my spa

[poffner]

I have a 1100 gallon custom tile inground spa. We have not been using much lately with the weather and have been keeping it covered most of time. Keeping the temp ~85 most of the time. I have noticed that my free chlorine levels have been off the charts. We have a salt system and I have turned the generator way down. WE have a service who comes every other week and I take care of it in between. The free chlorine level today was in the 40 ppm range. I was thinking of using thiosulfate to bring this down. Is this the best way to do this--or should I keep it uncovered and see if it will come down on it's own. This level is also interfering with other measurements but i think my TA is quite low as well--at least by strip measurement. I usually use the Taylor 2006 DPD test kit for more exact measurements. My pH level is high as well--at 8.4. This seems common with the salt system and I am constantly adding acid. I can't do an acid demand test right now as the high chlorine level interferes with it. I have also noticed the water is foaming a fair amount now as well.
Any help/advice is appreciated. Thanks!

Pat

 

[Jimrahbe]

Pat,

Welcome to TFP... a great place to find the answers to all of your "Mile High" chlorine level questions...

I would just turn off the SWCG and take the cover off when the sun is shining for a couple of days and see where that gets you.

pH measurements when the FC is above 10 are not accurate, so I would not worry about that until you can get the FC below 10.

Thanks,

Jim R.

 

[tim5055]

Welcome to the TFP pool! :splash:

Throw the strips away, they are worthless. Use your Taylor drop based kit to determine your TA.

But, you confuse me - you say you have a "Taylor 2006" but then say "DPD test kit". The Taylor K-2006 is a FAS/DPD test kit. It has a powder you place in the water sample to turn it pink then drops to make it go clear. Is this what you have and are using? The "DPD test kit" is a color match chlorine test.

Chlorine over 10 will cause a false high pH reading.

How about a full set of tests using the drop based tests:

FC
CC
pH 8.4
TA
CH
CYA

 

[poffner]

Thanks for your response. I only use the strip for a fast estimate--it helps me to sometimes to use the drop test with a lower volume of reagent when expecting a high result. I tried lowering the salt generator(Pentair IntelliChlor) output to very low and uncovered the spa for 4-5 days. My free chlorine levels have still been in the 30-35 ppm range with negligible combined chlorine. I have actually used both Taylor kits. I originally was using the 2006 but was concerned my reagents were bad--giving me the high readings. So I bought FAS/DPD kit(which i like better) and it confirmed the high free chlorine levels. I didn't do the whole battery of tests because the high chlorine levels seemed to interfere with the color changes. The pH was from a Hach digital tester. I got frustrated by the chlorine levels not going down from sun exposure and yesterday added some thiosulfate-I went on the conservative side so as not to overshoot. Unfortunately I'm on call in the hospital until tomorrow--then I will retest everything if the Cl levels are down.
Any other suggestions would be greatly appreciated.

 

[Jimrahbe]

p,

How is your cell connected? The cell will produce chlorine as long as your pump is running. How long do you run the pump each day?

Even an IC 20 will produce an FC increase of 76 ppm if you run it at 100% for 24 hours. You need to turn the cell off, not just lower the output.

Thanks,

Jim R.

 

[poffner]

maybe that's the problem. I have three pumps: one for the water feature which has been turned off and drained for the winter, a VS spa pump and a booster pump that gives us high output for "therapeutic massage" effect. The spa guys have programmed the booster pump to run for 15 minutes or so every 3 hours for freeze protection. Previously, it only ran when we manually turned it on. I'll have to check that out. Thanks!