Why is my chlorine level not decreasing?

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PT8787

Member
Jul 14, 2023
6
Sacramento California
We have a 10k gal salt water pool. I used the Taylor K-2006 test kit, the FAS-DPD one, to measure FC 10 ppm and CYA < 30 ppm (too low for the test to report anything). I took a sample to the pool store and they reported CYA of 11ppm. After reading a lot of the articles and forums, I'm sure I'll get recommendations to up the CYA right away, but before I change anything I wanted to bring down the FC level. I turned off our SWG yesterday morning and tested the chlorine at various times yesterday and today and the FC level hasn't budged a bit. It was 10 ppm 24 hours ago and is 10 ppm now.

I though that with a low level of CYA I'd see our FC level drop pretty fast. Our pool gets full sun and the UV index is 10 right now. Any thoughts on why the FC level isn't decreasing? Our SWG is a Pentair Intellichlor IC40. It is controlled via an Easy Touch. I turned it down to 0% and checked the generator to see that the output dropped to 0% according to the indicator lights. We don't have any other source of chlorine for out pool. Am I just being impatient? Everything I've read made it sound like the FC would drop pretty fast in direct sunlight.
 
PT8787 said:
We have a 10k gal salt water pool. I used the Taylor K-2006 test kit, the FAS-DPD one, to measure FC 10 ppm and CYA < 30 ppm (too low for the test to report anything). I took a sample to the pool store and they reported CYA of 11ppm. After reading a lot of the articles and forums, I'm sure I'll get recommendations to up the CYA right away, but before I change anything I wanted to bring down the FC level. I turned off our SWG yesterday morning and tested the chlorine at various times yesterday and today and the FC level hasn't budged a bit. It was 10 ppm 24 hours ago and is 10 ppm now.

I though that with a low level of CYA I'd see our FC level drop pretty fast. Our pool gets full sun and the UV index is 10 right now. Any thoughts on why the FC level isn't decreasing? Our SWG is a Pentair Intellichlor IC40. It is controlled via an Easy Touch. I turned it down to 0% and checked the generator to see that the output dropped to 0% according to the indicator lights. We don't have any other source of chlorine for out pool. Am I just being impatient? Everything I've read made it sound like the FC would drop pretty fast in direct sunlight.
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Well, at least you have a SWG that is large enough for your pool...4x the size of your pool actually. That's a good thing! That being said, when you have a SWG your CYA range should be 60-80. Why not just increase your CYA to handle your FC level? That is unless you're simply trying to dial in your SWG. I don't have that particular brand of SWG but several others on this forum do and I'm sure they can chime in. What were you running it at? I see that it produces 1.47 lbs of chlorine/day at max output for 24 hrs. A pool your size running for 24 hrs would produce: 18ppm at 100% output, 8.8ppm at 50% output, and 4.4ppm at 25% output.
 
I am trying to dial in my SWG, that's exactly it. I'm also new to pool care and just wanted to see if what the documentation says is true, that is I keep reading that you can lose 90% of the FC in 2 hours in direct sunlight with no CYA. I do have some low level of CYA so I didn't expect it to happen quite that fast, but it leaves me scratching my head that my FC hasn't gone down at all over 24 hours. I would like to better understand what's going on before I add anything to the pool. I'm not sure why I should be in such a hurry to add something to stabilize the chlorine if it is already extremely stable.

The back story is that we've been paying a pool service to take care of our pool since we bought our house a couple of years ago. Earlier this month bought I test kit and started reading up on pool maintenance thinking I'd start doing it myself to save some money. However after testing our water I realized I should be doing the pool maintenance because our pool guy is not doing his job right. I tested our water and our numbers were way off from the norm. pH of 6.3, alkalinity pretty much 0, CYA of 11, etc. I got his manager out last week and he fixed most of the pool chemistry, but left the CYA alone. The SWG was running at 100% output and the manager lowered it to 60%. Needless to say I've stopped our pool service.

Last week after a few days of the SWG running at 60% I kept seeing high chlorine levels (or high for the level of CYA) and that's when I realized what you guys already figure out, that our SWG is super sized for our pool so should be running at a really low rate. So I'm trying to get a handle on what it should be set at. I'd like to adjust it and actually see and measurable change in the FC in the pool.

I think with the SWG running at 100% it was causing the pH to skyrocket and the pool guy was just dumping in loads of acid each week to combat it, until he over did it, which was how the pool ended up where it was. Not sure why they never added any CYA at the beginning of the pool season. I asked the manager and he basically dodged my question, or said the same thing I did above, which was we seem to have no problem generating and keeping chlorine so high we don't need to add any CYA. I'm not saying I trust his judgment on that, but I also need to learn more before I start adding stuff to the pool that's hard to take out.

I can take a photo of the chlorine test, but it's the FAS-DPD one that turns from pink to clear after a certain number of drops. Not sure how helpful a photo of that will be. I can say I used 10ml of water, 2 scoops of the powder, and have had to add 20 drops to get the color change. So 20*0.5 = 10 ppm. Hopefully that makes sense if you're familiar with the Taylor test kit.
 
Don't worry too much about your apparent lack of FC loss. I am not sure exactly where the issue is but, trust me that the FC WILL COME DOWN.

why I should be in such a hurry to add something to stabilize the chlorine if it is already extremely stable.
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I hear you but it is coming down and will continue to do so.

I would suggest you ignore that for now and go ahead and add 30 CYA to your pool. It may be helpful if you could post you other results.....
pH - ??
TA - ??
CH - ??
 
duraleigh said:
Don't worry too much about your apparent lack of FC loss. I am not sure exactly where the issue is but, trust me that the FC WILL COME DOWN.


I hear you but it is coming down and will continue to do so.

I would suggest you ignore that for now and go ahead and add 30 CYA to your pool. It may be helpful if you could post you other results.....
pH - ??
TA - ??
CH - ??
Click to expand...
pH - 7.4
TA - 80
CH - 250
Combined chlorine - 0
Sodium Chloride - around 4000 (used test strip, SWG says salt level is good)
 
PT8787 said:
we seem to have no problem generating and keeping chlorine so high we don't need to add any CYA. I'm not saying I trust his judgment on that, but I also need to learn more before I start adding stuff to the pool that's hard to take out.
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Your SWG is evidently powerful enough to keep adding chlorine but it’s going to burn off very fast without stabilizer (CYA). The trouble may be that the pool store test for CYA (and everything else) tends to be really bad. It’s possible you have more than 11ppm in the water and that’s slowing the chlorine degradation. You should test CYA again with the Taylor kit.

The other possibility is that the SWCG is not really off. They automatically turn on and off on a cycle and if you look at it during the “off” time you might assume it’s always off. Also I’ve read about some automation systems say they are at 0% but still come on periodically. No idea if that’s the case here or not.
 
PT8787 said:
I can say I used 10ml of water, 2 scoops of the powder, and have had to add 20 drops to get the color change. So 20*0.5 = 10 ppm.
Click to expand...
Save your powder! All you need is a heaping spoonful of it...just one not two. You'll get your SWG figured out in due time. Ditch the test strips for testing your salt and get the K-1766 to add to your current Taylor kit. Waaaaay more accurate. Get 30ppm CYA in there as @duraleigh suggested.
 

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