Can’t raise chlorine

cdan16

Member
Jun 24, 2016
16
Philly Suburbs, PA
Hi all. Think I am dealing with a Chlorine lock situation and could use some advice. Pool professionally opened on 4/21 and non-chlorine shock was added.

4/27 Tested FC 0.3 | CC 0 | CYA I put down at zero as water was crystal clear up to the top of test tube | pH off the charts basic | TA 125. Added 96oz of 12.5% chlorine | 79oz of 20* Muriatic. Ordered stabilizer.

4/28 Tested FC 0.4 | CC 1.6 | pH 7.2. Added 177oz of 12.5%. Ordered new DPD powder.

4/29-30 rain

5/1 Tested FC 0.1 | CC 2.4 | CYA 0 | pH 7.9 | TA 105 Added 4lb dry CYA (pillow case in front of return method) | 256oz of 12.5% (evening)

5/2 Tested (morning) FC 0.3 (!) | CC 3.0 | CYA 20ish | pH 7.4No additions.

Using Taylor k-2006 for testing and new SPD powder over last couple of days.
Pool water is very clear throughout and weather is chilly (though I optimistically fired up heater and am keeping water at 65 degrees). So my questions are:

1) could my 18k gal pool really be burning through this much chlorine? I added 2 gallons at 5:45 pm yesterday (overcast evening sunset at 8ish) and tested 0.3 ppm FC this morning (around 11:45am). Pool Math tells me I’d only need 1.5 gal to get to 10ppm I realize CYA is very low (still not sure why that would be since I didn’t drain/refill more than a few inches over winter. Could this explain such a big drop?

2) Do I need to add yet more Chlorine? I’ve added more than four gallons already. I’m not made of chlorine, you know. Bonus: just called supplier and they are SOLD OUT of chlorine.

3) most of the CYA was gone from pillowcase this morning but reading still only at 20. I’ve read that it takes longer to show up on test but does that mean I should wait to add more chlorine?

4) what’s up with CC going up and up? Do I need to just ad a ton of chlorine to break through? Pool store from which I purchased chems suggested adding 5gal all at once. This seems insane. Thoughts?

5) side note: could the CYA have dropped my pH by 0.4 overnight? I read that it doesn’t have that big of an impact.

any help would be greatly appreciated. Thanks in advance.

Dan
 
Last edited:

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
32,581
Laughlin, NV
You say your water is clear. No debris on the floor in the morning. Can easily see the bottom of the deep end, details of the drain covers?
The non-chlorine shock is showing up as CC and messing with your testing. It will take time for that to dissipate.

With little or no CYA FC is burned off quite quickly by the sun.
Once the CYA is fully dissolved, wait 24-48 hours and then test for it. Target 40 ppm CYA
CYA is acidic and will drop pH some.

Chlorine 'lock' is a bit of a misnomer. Do not do a mass dump of liquid chlorine.
Do a Overnight Chlorine Loss Test tonight if you can.
 

cdan16

Member
Jun 24, 2016
16
Philly Suburbs, PA
You say your water is clear. No debris on the floor in the morning. Can easily see the bottom of the deep end, details of the drain covers?
Drain cover clear. Very little debris on bottom (vacuumed on 4/28 but subsequent wind blew some more in). Water totally clear.

The non-chlorine shock is showing up as CC and messing with your testing. It will take time for that to dissipate.
Good to know
With little or no CYA FC is burned off quite quickly by the sun.
I get it but that quickly??
Once the CYA is fully dissolved, wait 24-48 hours and then test for it. Target 40 ppm CYA
CYA is acidic and will drop pH some.
ok will do.

Chlorine 'lock' is a bit of a misnomer. Do not do a mass dump of liquid chlorine.
Do a Overnight Chlorine Loss Test tonight if you can.
Ok will test and won’t indiscriminately add chlorine. I don’t have much left to be honest I don’t have much left to be honest my supplier is out.
 

cdan16

Member
Jun 24, 2016
16
Philly Suburbs, PA
Half life of FC in pool water with 0 CYA is about 50 minutes with sun shining on the pool surface.
Wow! So definitely possible for all chlorine to go away no matter how much I add. Still, CYA was at 50 on September 3, 2019 so I wonder how it got so low considering I didn’t drain refill but here we are I suppose.
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
32,581
Laughlin, NV
In your area do you not winterize by lowering your pool water volume? And then during winter does not your pool refill and possible over flow due to snow melt and rain? All those things dilute the CYA level. Plus CYA does degrade just a bit. So not unusual to have low to zero CYA in the spring.
 

SouthVirginiaPool

Silver Supporter
Apr 26, 2020
104
Chesapeake, Virginia
New guy here so I can only tell you my struggles. New pool, CYA was 5 ppm (I didn't know better) and pool store said to put 4 lbs of shock in. Chlorine level would get above 5 (based on test strips), then go to 0.5 ppm within 3 days. Did this 3 times before I got my own test kit, added CYA to 40 ppm, and now I have to turn off my SWCG for a few days to drop down to target (was as high as 10). CYA is REALLY key. No longer bother with pool stores and the Walmart guy tried to sell me algicide (I wanted bleach) - but because the bottle said it was "Clorox" brand - it had to be bleach (it wasn't). Good luck.
 

cdan16

Member
Jun 24, 2016
16
Philly Suburbs, PA
In your area do you not winterize by lowering your pool water volume? And then during winter does not your pool refill and possible over flow due to snow melt and rain? All those things dilute the CYA level. Plus CYA does degrade just a bit. So not unusual to have low to zero CYA in the spring.
Yeah I do but only to get it below the skimmer. Cover pump should be getting rainwater before it gets into the pool mostly. Let’s see what happens now that I’ve added CYA. Thanks for all of your help!
 
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cdan16

Member
Jun 24, 2016
16
Philly Suburbs, PA
OK - just an update: I added a total of 5.5lb of CYA over the course of a couple of weeks and now I'm testing right at 45. As expected FC has stabilized somewhat though I still have to add some almost every day. I'm now thinking I've underestimated my pool size since chemicals don't have the impact Pool Math tells me they should. Next step is to get TA down and CH up a bit. Thanks again for all the advice. PS: I just realized anyone can go in and see my PoolMath logs so I guess I didn't need to retype them above. Live and learn, I suppose.
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
32,581
Laughlin, NV
No need to focus on TA. Test it whenever your pH reaches 8 and you need to lower the pH. You need the TA value for Poolmath to determine how much acid to add.

The last CH test result I see is 215. That is not a value you can get from one of our recommended test kits. So you might want to test that again before you add any calcium.
 

cdan16

Member
Jun 24, 2016
16
Philly Suburbs, PA
No need to focus on TA. Test it whenever your pH reaches 8 and you need to lower the pH. You need the TA value for Poolmath to determine how much acid to add.

The last CH test result I see is 215. That is not a value you can get from one of our recommended test kits. So you might want to test that again before you add any calcium.
I’m using the Taylor K-2006 and I was estimating that the value was somewhere between 210 and 220. It wasn’t completely blue at 210 and was very blue at 220. I’m following pool math’s suggestion and aerating to lower TA and raise pH but, as you say it probably doesn’t matter all that much.

Thanks so much for your help!
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
32,581
Laughlin, NV
Pick the very blue.

With drop based tests, if you add drops until the last drop makes no color change, and subtract that last drop, you will have the correct result.