New SWG Pool - Rising Chlorine

[Steve-D]

We have a new 20,000 gallon SWG Gunite Pool filled on 5/6 and the pump running continuously since then, mostly at low speed (1500-1700 rpm) when not in use or while cleaning. 18 bags (@ 40 lbs each) of salt was added on 5/27 which works out to about 3400 ppm. The Intellichlor IC40 label says the ideal is 3600 so its close. The SWG is set at the lowest (2%) chlorination rate.

We had been managing the Cl level manually prior to adding the salt and after a some wild fluctuations (mostly from trying to get the CYA level stable) we managed to get Cl to around 4.0 and slowly dropping with the expectation that the level would drop naturally with sun and use until we hit a target closer to 2.0 as recommended by the installers. FC had been roughly constant at between 3.5 and 4.0 going into and through Memorial Day w/e where the pool saw much use. It has been cool and gray since then, however, so the solar cover has stayed on and we haven't been in the pool now for the last 2 days. We are still running the pump continuously and today the FC measured at 6.0.

According to another post the SWG will add chlorine as long as its running so an increase like this would be expected. It was suggested that the only way to bring down the Cl is to run the pump less frequently and/or turn off the SWG for a few days...is that the case here? This is not our first pool but it is our first SWG pool

Current Chemistry is noted below.
I don't have the test reagents for salt (yet) but per what was added it should be about 3400 ppm.

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Mendon MA
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Build Type: Plaster
Volume: 20000 gallons
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Latest Test Result Summary:
FC: 6.0 (an hour ago)
CC: 0.0 (an hour ago)
pH: 7.7 (an hour ago)
TA: 100 (2 days ago)
CH: 240 (2 days ago)
CYA: 60 (2 days ago)
==========================================
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Test Results 05-31-2022 @ 07:15 AM
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Free Chlorine: 3.5
Combined Chlorine: 0.5
pH: 7.6
Total Alkalinity: 100
Calcium Hardness: 240
CYA: 60

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Test Results 05-30-2022 @ 07:31 PM
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Free Chlorine: 3.5
Combined Chlorine: 4.0
pH: 7.2

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Test Results 05-28-2022 @ 10:45 AM
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Free Chlorine: 3.3
Combined Chlorine: 0.0
pH: 7.8

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Chemical Addition 05-28-2022 @ 08:30 AM
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+ 13 FluidOunces of Baume31

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Test Results 05-26-2022 @ 08:15 AM
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Free Chlorine: 4.0
Combined Chlorine: 0.0
pH: 7.6
Total Alkalinity: 100
Calcium Hardness: 240
CYA: 50

 

[pjt]

18 bags (@ 40 lbs each) of salt was added on 5/27

New plaster should cure at least 30 days before adding salt. The salt addition was premature.

How are you testing?

 

[Steve-D]

I am testing with a TF-100 for Cl and CYA and using the Taylor (5000?) for PH, TA and CH...the installers provided that kit and the reagents are newer.

[edit] I know that salt was about 1 week early by most (but not all) guidelines and my wife was insistent on officially opening the pool for Memorial Day weekend entertaining. It all would have been on schedule for that except the colder than hoped for April and then rains here in mid/late April pushed the plastering schedule back 1 week.

 

[jark87]

First of all, FC at 6 is perfectly fine. I don’t know why your builder would recommend 2 - that’s too low. I try to keep FC in the 7-9 range. Take a look at this: Chlorine / CYA Chart

Second, check out the Pool Math app to see how much chlorine your SWCG will add based on run time and %. I find it hard to believe that 2% would add 2.5 in a day, but with the cover on, no sun exposure and no bather load or contaminates, maybe it’s possible. I’m not familiar with your cell, so I could be wrong. There are experts here who can tell you what the chlorine output of your cell is based on % and run time.

Last, you should be able to turn your cell off. If tests show a chlorine rise with the cell off, something else is wrong, like testing.

The good news is that your chlorine level is fine, assuming the test is accurate, and if you can get away with running your SWCG at a low rate, you’ll extend the life of your cell.

 

[PoolStored]

The SWG is set at the lowest (2%) chlorination rate.

Something is not right. With IC-40 (1.4 pounds/day) running at 2% for 24 hours will add .2 FC in a 20K pool.

Can you recheck your settings?

 

[Steve-D]

I will double check my measurements end of day but the Intellichlor settings are as noted above: Salt "good" with flashing green LED and the % Indicator at 2%. I may have under-read some earlier FC tests , but probably not off by more than 0.5 ppm (1 more drop of R-0871 to get an "absolutely" clear reading). I will monitor and work at consistency in my testing. The drop test is new to me and I tend to forget to factor in the CYA adjustment for the optimal target reading. At 6.0 FC and 60 CYA I'm not going to fuss over it unless I see that the #s are changing unexplainedly...and being more consistent in my test procedure will give clarity to that.