Rapid pH increase with SWCG

flippinGeo

Bronze Supporter
Oct 8, 2016
81
Maryland
Day 9: +0.2? pH (8.2- 8.4), no change TA (80), +30 in CH (500).

ok this CH rise is odd. I even tested it twice to confirm the endpoint. WTH is going on?
 

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flippinGeo

Bronze Supporter
Oct 8, 2016
81
Maryland
So here is the only thing I can think that is different this year other the the SWCG. I was unable to find pure calcium chloride flakes like usual so per another post I purchased some pellets that were not pure CC. Unfortunately it doesn’t provide a % breakdown of the ingredients. Maybe this is the culprit? Though I wouldn’t understand how.
 

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JamesW

TFP Expert
Mar 2, 2011
28,256
I don't think that the calcium chloride is a problem.

The pH looks pretty close to yesterday.

Maybe get a pH meter to help monitor the pH more accurately.

I really do not understand why the readings are changing like they are.

Definitely a mystery.
 

flippinGeo

Bronze Supporter
Oct 8, 2016
81
Maryland
i assume now you are ocd about the test sample water level and adding drops slowly
were you always very careful or a bit
"that's near enough" on the samples
not trying to point a finger, just looking for an easy answer to past discrepancies
So I’m a scientist by trade, albeit not a chemist. That said, I’m pretty precise with measuring. Sure I’m not using syringes to add water, maybe I'm not holding the tube 100% level, and maybe the meniscus is a bit above or below the line sometimes, but I’m pretty diligent. I rinse the tubes every time with the pool water and perform my dips at elbow deep (~18") always at the same spot in the pool (deep end that has plenty of movement from the deep end return). Fluctuations of 10, or even 20, pts doesn’t concern me as I understand there is an expected margin of error in these drop tests. But the incredible rise of pH, TA, and CH while I was away on vacation cannot be attributed to measurement error. And my constant rising of pH throughout the season...

I left for vacation on 9/11. On 9/10 this is where my numbers were:
  • FC - 6.0
  • pH - 7.3
  • TA - 65
  • CH - 430
  • CYA - 80
  • SALT - 3800
I returned on 9/19, so 10 days without human intervention, and my numbers were:
  • FC - 3.0 (-3.0) - Explained by my reduction in pump run-time and SWCG output
  • pH - 8.? (+ >= 1.0) - In my return test I estimated 8.4, I dosed with 1 gal and it reduced still above 8.0 so I assume it was actually higher.
  • TA - 120 (+ 55) - ?? My TA has always been fairly stable at a range of 60-80. I expected to come up to high pH, but this was a big surprise. I don't believe this was a measuring error, validated by the 2 large acid doses that brought it back down to "normal" range (60-80).
  • CH 490 (+ 60) - ?? Again, I cannot explain the rise in CH while away. Unless a neighbor came by and dumped 10lbs of CaCl in my pool it must have been extracted from the pool or scale. I last dosed CaCl on 7/29 which aligns with my measurements up until I left. However, once I left I cannot explain the rise in CH and TA.
If you look back through my historic log (+1 year) you'll see that I was a bit obnoxious with balancing the water (i.e. dosing acid at 7.8 just to get to 7.6, but even then it was infrequent because the pH was so stable. Take a look starting at 5/21/20 pH was at 7.3 (not sure why I dosed down so low be regardless)... pH remained the same all they way through 6/27/20 when I dose Borax to bring my TA up. But even then my pH remained stable at 7.6 through closing on 10/21/20. Another section to look at is 9/13/19-9/22/19. This was the same annual vacation we just took 2 weeks ago. I left with a pH of 7.8, dosed 32oz of dry acid, then returned 10 days later to a pH of 7.6. I would define this as stable.

I understand SWCG do raise pH, so I'll be dealing with acid more often than I did before. But my rise of an avg of ~.2 daily is, in my opinion excessive and really shouldn't be the case.

Please understand I'm not trying to argue with you. I understand this is a chemistry issue and not some weird anomaly where I'm being punished for past wrong doings. Just like you, I'm really trying to figure out what is going on so I can fix it. I'm 100% certain this is result of something I've done. I just need to figure out what that is so I can avoid it and get this Dang pool in some state of stability. This really has been the worst pool season I've had with this pool since we moved here in June 2013 and that includes 1 season of battling 2 instances of white water mold. The only thing different this year is SWCG. For next year I'm half tempted to disconnect it and go to liquid chlorine. I'll never go back to the tabs.

I appreciate all of your guys help. This forum is great, always has been. I appreciate @JamesW taking the time to explore this with me.
 
Last edited:

mknauss

Mod Squad
TFP Expert
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May 3, 2014
44,389
Laughlin, NV
Pool Size
6000
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Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
It is true that pH will tend to stabilize at 7.8 or so with a SWCG. Likely due to the mild aeration caused by the hydrogen bubbles.
 

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JamesW

TFP Expert
Mar 2, 2011
28,256
To me, it looks like scale or plaster is dissolving, but this would be a lot of dissolving with no real obvious explanation.

Definitely outside of all normal situations.

This is about 6 standard deviations to the right of the mean.
 

flippinGeo

Bronze Supporter
Oct 8, 2016
81
Maryland
Day 10: pH still appears to be rising. No change in TA or CH.

Not sure what the measurement is but it took 4 drops of acid demand reagent to reach 7.8, and the end point is approaching purple.

Do I hold or do I dose acid? I’m out of ideas now.
 

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JamesW

TFP Expert
Mar 2, 2011
28,256
The pH does not look to be that high to me.

Since it is going out of range, I would add enough acid to keep the pH at about 7.9 to 8.0.

Once it goes out of range, it can get away from you.
 

flippinGeo

Bronze Supporter
Oct 8, 2016
81
Maryland
TA and CH are both on rise again. I didn’t even test yesterday and still haven’t dosed acid since my interpreted my 8.6 the other day. Chances are it’s now 8.8 or above. I hate to say it, but I’ve lost motivation.

Im out of ideas. None of this makes sense to me, and seems no one else. Im defeated and now I need to prepare to close this thing with no positive vibes to start next season.
I guess I’ll just dump this water and get fill water again next season. But that approach is just not sustainable as it’s ridiculously costly.

if anyone has any other thoughts. Please share. Thank you everyone for your help so far. I just wish we could figure this out.
 

Bperry

Gold Supporter
Aug 20, 2020
1,012
Knoxville, TN
Pool Size
27000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
CircuPool RJ-60
TA and CH are both on rise again. I didn’t even test yesterday and still haven’t dosed acid since my interpreted my 8.6 the other day. Chances are it’s now 8.8 or above. I hate to say it, but I’ve lost motivation.

Im out of ideas. None of this makes sense to me, and seems no one else. Im defeated and now I need to prepare to close this thing with no positive vibes to start next season.
I guess I’ll just dump this water and get fill water again next season. But that approach is just not sustainable as it’s ridiculously costly.

if anyone has any other thoughts. Please share. Thank you everyone for your help so far. I just wish we could figure this out.
I would not assume your pH is 8.8 since you can’t actually measure it. It doesn’t tend to rise linearly like you’re projecting. Mine will shoot up really fast to 7.8 and then slows way down. I’d almost be tempted to get a pH test somewhere else to see how far above 8 it really is.

also, your log note says you’re trying for a FC of 3 but your CYA is 80? That’s pretty low with that much CYA in the water.
 

flippinGeo

Bronze Supporter
Oct 8, 2016
81
Maryland
I would not assume your pH is 8.8 since you can’t actually measure it. It doesn’t tend to rise linearly like you’re projecting. Mine will shoot up really fast to 7.8 and then slows way down. I’d almost be tempted to get a pH test somewhere else to see how far above 8 it really is.

also, your log note says you’re trying for a FC of 3 but your CYA is 80? That’s pretty low with that much CYA in the water.
I didn’t post a picture of todays test, but the endpoint is now purple. You‘re right though, I have no idea what it is, but it’s substantially above 8. The amount above 8 is only important for determining the acid dose. My issue is rapid rise in pH, TA and apparently CH. Its unexplainable and in order to maintain it I basically have to dose acid everyday.

as far as FC target, you’re right. Adjusted my target to 4. But FC is easy, and not my main concern here. I’ve not had an issue yet this season with FC once I figured out pump timing and output.
 

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