Combined Chlorine questions

Transient

Active member
Feb 3, 2021
29
BC, Canada
Hello. I have an in-ground salt water pool owner (see signature). Pool is 18 years old, but this is my first year of ownership.

I had a pool company open the pool for me at the end of April. He shocked the pool and the water cleared right up. After a couple days, I put the solar cover on and it has been on non-stop since. The water still looks clear.

The water has finally reached a decent temperature and this weekend is looking to be hot outside. I was hoping to use it, so I took some tests today:
2.5 Free Chlorine
7.5 Combined Chlorine
7.8 pH
190 Total Alkalinity
275 Calcium Hardness
0 CYA

Now finally on to my questions:
I know SLAMing the pool will eliminate CC, but as I was hoping to use the pool this weekend, is it safe to leave this until Monday and use the pool?
Is it possible the CC is high because the solar cover has been on for a couple weeks non-stop? Should I take it off and let the UVs do their work?

I know I also need to adjust the pH/TA and add some stabilizer. Am I correct that I should adjust pH/TA first, then SLAM, then finally CYA after FC is back to normal?
 

magiteck

Gold Supporter
May 20, 2020
580
Neenah, Wisconsin
Pool Size
13600
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Vinyl
Chlorine
Liquid Chlorine
I would leave the cover off, add 30ppm CYA, add some LC, and re-test after a day in the sun to see what CC burns off. If the CCs go down, then do an Overnight Chlorine Loss Test to determine if you need to SLAM.

If the water is clear I’d anticipate any necessary slam would go quick.
 
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IceShadow

Gold Supporter
TFP Guide
Jun 8, 2019
2,612
Milwaukee, WI
Pool Size
20000
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Chlorine
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It is safe to swim in a pool at SLAM level FC, so long as you can see the entire bottom of the pool.
 
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Transient

Active member
Feb 3, 2021
29
BC, Canada
How are your numbers looking today?

Thanks for checking in again. I added the CYA as you suggested. CC went even higher, up to 9.0. FC was still 2.5. However, right after I responded to you, it clouded over and a thunderstorm blew in, so I don't think it was a fair test.

I had the cover off all day yesterday. It was hot and sunny the entire day, but by the time the end of the day rolled around, I had forgotten to test it. And by forgotten, I mean we had a few too many drinks. Sorry, I hate to ask for help and then not follow the advice given.

I'm going to do a test again this morning to see where we're at, although we also used the pool yesterday so I imagine CC could be higher from that. The water still looks clear. We plan to use it again today as it is the last nice day in the forecast. If CC has gone down, then I'll do the overnight FC loss test as you suggested.

That high CC may cause some burning eyeballs. And some smell.

You'd think so, but there is no smell at all. We ended up using the pool all day yesterday, nobody complained of anything. No red eyes, no smells, no irritated skin. If CC was half this amount in my hot tub, it'd be choking us out, but this seems fine. I'm not really sure why that is.

It is safe to swim in a pool at SLAM level FC, so long as you can see the entire bottom of the pool.

Is that right? The booklet in the Taylor test kit says not to resume swimming until FC drops to 5. Are they just being over cautious?
 

IceShadow

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TFP Guide
Jun 8, 2019
2,612
Milwaukee, WI
Pool Size
20000
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Liquid Chlorine
The Taylor book follows most of the pool industry with outdated ideas of pool chem levels. They don’t acknowledge the CYA/FC relationship at all.

CC of 9 would give a huge odor / smell to it. I am suspecting something is wrong with your testing method, or some other chemical was added in the past that is reading as high CCs. Have you added any non-chlorine shock in the past?
 

Transient

Active member
Feb 3, 2021
29
BC, Canada
The Taylor book follows most of the pool industry with outdated ideas of pool chem levels. They don’t acknowledge the CYA/FC relationship at all.

CC of 9 would give a huge odor / smell to it. I am suspecting something is wrong with your testing method, or some other chemical was added in the past that is reading as high CCs. Have you added any non-chlorine shock in the past?

I was also wondering if the CC test is giving a false reading. I am following the Taylor directions exactly and I use precise measurements (level surface, verify sample level is dead on the line). I use the same kit to test my hot tub, which doesn't give an abnormal reading, so I think the kit itself is fine and the reagents are fresh/not expired.

It's possible some other chemical was added to the water. I took possession of the house in January and so I have no idea what was added prior to that. The water was drained below the jets for the winter, but that still leaves a lot of water. Also, I had a pool company open the pool for me at the end of April and he added a bucket of something (I assumed shock / cal hypo, but I can't say for certain).
 

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IceShadow

Gold Supporter
TFP Guide
Jun 8, 2019
2,612
Milwaukee, WI
Pool Size
20000
Surface
Vinyl
Chlorine
Liquid Chlorine
It’s possible they added something that is registering as CC. Over time whatever it is will break down. I guess I would worry about the other numbers for now and keep an eye on the CC but not stress it. Still leave it open to the sun to burn off the CCs.
 
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Transient

Active member
Feb 3, 2021
29
BC, Canada
It’s possible they added something that is registering as CC. Over time whatever it is will break down. I guess I would worry about the other numbers for now and keep an eye on the CC but not stress it. Still leave it open to the sun to burn off the CCs.
Thanks, I think you're right. Today's reading is 2.0 FC and 8.0 CC. The water still looks clear and no smell at all.

Tonight I'll do the overnight chlorine loss test as magiteck suggested and see what happens.
 

Transient

Active member
Feb 3, 2021
29
BC, Canada
FC is pretty low. Be sure to follow recommendations in the FC/CYA Chart.
When I tested the CYA a few days ago, it was at zero, so I'm in the process of raising that. I raised it to 30 and will keep going until I get to 70.

My understanding was the FC will come up a bit once the CYA is at the proper level and the SWCG won't have to work as hard. Does that sound correct?
 

CrystalRiver

Well-known member
Jun 19, 2020
648
Massachusetts
Hold off on adding any more CYA. One, if you need to SLAM, you want to do that at CYA 20 or 30, ideally. Two, it takes about a week after adding before you can get a reliable CYA test result.
 
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