Why my pool doesn't hold chlorine?

Justify

Well-known member
May 7, 2019
49
Iowa
Our pool is SWGC. When I first tested with my brand new TF100 test one month ago (June 3), I had high CC (2.5), TA (180) and zero CYA. FC was 0.5. I got ready to SLAM, gathered all the chemicals needed and before adding them, I tested again (June 5), and CC was 0.5 this time (FC=2), so I didn't perform SLAM after all.
I slowly keep adding stabilizer (I know my goal is CYA = 70, but I was warned not to raise it too fast, in case I would need SLAM), but for some reason, I basically don't have chlorine. Three days ago (June 29) I added liquid chlorine (bleach) to raise FC to 3, and also CYA (sock in my two skimmers, two pounds each so 4 pounds total) to raise CYA to 40. The next morning, I tested FC and it was only 1.5. It took 2 days for all the stabilizer dissolve and when I checked this morning, CYA was 40 as expected. I also noticed this morning that pH was somewhat lower than normally (around 7.0 vs 7.2-7.5). FC was 0.5 this morning (or less - barely noticeable pink which cleared after first drop)
What could cause the constant chlorine loss? Low CYA maybe? Shall I add bleach again? Aim for FC 3? Or more?
I also plan to add some baking soda to raise pH. Not CYA tonight - I want to test tomorrow morning again, which would be 36 hours after all stabilizer dissolved, and add more stabilizer then. Shall I aim for 70 this time?
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
33,279
Laughlin, NV
You most likely have algae and need to follow the SLAM Process

Do not add baking soda. It raises your TA. A month ago in your Poolmath log, you show a TA of 180.

If you add your tests as you do them to Poolmath, it is much easier to guide you.
 

Justify

Well-known member
May 7, 2019
49
Iowa
OK.
Should I go with CYA 40 from this morning or wait till tomorrow to make sure all the stabilizer I used is back in the water, and test CYA again? I figure it takes awhile since the socks are in skimmer, not in front of the returns, so it needs go throough filter right? It only fully dissolved 24 hours ago (tested 12 hours after dissolved)
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
33,279
Laughlin, NV
You should start the SLAM assuming 40 ppm CYA. So SLAM level FC is 16 ppm. Add chlorine now to that level and maintain it.

Test the CYA tomorrow or Saturday to confirm the level.
 

Justify

Well-known member
May 7, 2019
49
Iowa
Thanks @mknauss
I tried to log my new test results, but it says 'to store unlimited logs, please subscribe to pool math premium'. When I click on 'subscribe', it kinda seems to ignore me, if i click on 'restore subscription', it says 'no subscription found' :(
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
33,279
Laughlin, NV
OK -- so you did not sign up for the app, you are using the free version.

Up to you. $8 a year to store your data.
 

Justify

Well-known member
May 7, 2019
49
Iowa
@mknauss Sorry, one more stupid question.
You said "Add chlorine now to that level and maintain it "
I got the 'add chlorine' part, but what do I need to do to maintain?
 

Justify

Well-known member
May 7, 2019
49
Iowa
Thanks. Since it is already getting dark, I will probably start tomorrow morning to be able to test every few hours and adjust as needed. I may also need to buy more bleach.
Thank you!
 

Justify

Well-known member
May 7, 2019
49
Iowa
Or shall I just start with overnight loss test?
The article says the goal of SLAM is get clear water, CC 0.5 or lower and pass the chlorine loss test.
I do have crystal clear water and my CC level has been 0.5 or less since June 5.
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
33,279
Laughlin, NV
Sure. Do a OCLT. Raise your FC to at least 5 ppm tonight, circulate for 30 minutes or so, test FC, leave pump on overnight, and test before sunrise.
 
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Justify

Well-known member
May 7, 2019
49
Iowa
Here are my test results (and the procedure):
I poured the bleach by one of the returns (we have 3, I chose the deeper end one - where the depth gradually increases - the other two are by shallow water)
Tested about 40 minutes later (10:15pm):
by the return - 8.0ppm
by the skimmer opposite to the return - 7.5ppm
Morning test performed at 5:30 am:
by the return: 5.0 ppm
by the skimmer: 6.5 (maybe 6.0) ppm

So am I going ahead with slam?
The problem is, my husband turned on the automatic shock this morning. Not sure how it works.
So my immediate plan is:
test CYA to determine SLAM level
test FC, add bleach if needed, leave alone if higher than needed
Then keep testing FC probably every 4 hours and adding bleach if needed to reach the SLAM level
Is that a right way to proceed or did I miss something?
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
33,279
Laughlin, NV
You have a SWCG. It is best to turn it off or down to 0% generation during the SLAM Process

Your plan is good. Brush the pool really well at least once per day. Vacuum too unless you have a robot/pool cleaner.
 
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Justify

Well-known member
May 7, 2019
49
Iowa
@mknauss quick question.
Can I add bleach to adjust FC while robot is in the pool and cleaning? It is safe? Or do I need to wait till it finishes and is out of water?
(I just put our brand new Pentair SE Warrior in without realizing it will take two hours)
 

Justify

Well-known member
May 7, 2019
49
Iowa
Thanks. I removed the robot about half hour ago, tested water and adjusted.
First adjustment to raise FC to 16 ppm was at 3:40 pm today
At 10 pm it tested 12.5 ppm, and I adjusted it to 16ppm according to PoolMath (only 77 oz of 12.5% bleach needed this time).
I'll test again tomorrow early morning.