pH trends down...normal?

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Rumbleehockey03

Bronze Supporter
Jul 8, 2019
86
Central NC
Pool Size
12500
Surface
Vinyl
Chlorine
Salt Water Generator
SWG Type
Solaxx (Saltron) Reliant / Purechlor R5
Just a general question on pH since it’s the only thing that doesn’t stay maintenance free for me after using the tfp normal guidance. My pool pH always trends lower at all times of the year and I’m just wondering if there’s anything I can tweak to make it stay consistent, and it seems I read that most pools trend upward, not downward. In mid-summer I run a fountain 24/7 to keep water temp down and it actually perfectly balanced pH, but when it’s not going I have to add borax here and there to keep it up. Last full test results:
Salt 3200
Cya 70
Ph 7.2 (added 2lbs of borax today after this reading)
Ta 80
CH 125
FC 6.5
Cc 0
 
You are adding something acidic to lower your pH or you have low pH fill water.

You have no trichlor pucks in the pool?

What is the pH and TA of your fill water?
 
No trichlor, I have SWG and use granular cya when I need it. Just checked ph of fill water and it’s 7.5. Haven’t checked TA but I assume it’s zero because my TA stays consistent all year once it’s corrected after opening fill.
 
Rumbleehockey03 said:
No trichlor, I have SWG and use granular cya when I need it.
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How often do you add CYA? CYA is a mild acid and will lower pH.

Rumbleehockey03 said:
Haven’t checked TA but I assume it’s zero because my TA stays consistent all year once it’s corrected after opening fill.
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I am sure your TA is not 0. Recommended TA is between 50 and 100.
 
I added some cya after topping off when I opened the pool a couple months ago. Typically add maybe once per month or so as it drifts lower
 
Maybe a bit of additional clarification on the ph drift. Ph on 17apr was 7.2. On 28apr it was closer to 6.8 without having added any cya or fill water between that time, and minimal pool usage as well. It’s a slow drift down.
 
Just a wild guess here but if you are first testing FC using the FAS DPD powder then testing pH in the same vial and not properly rinsing the vial between tests you can skew your pH down significantly.
 
I do have the tfp kit so using different vials for ph and FC. Might just be normal for my pool...that answer won’t hurt my feelings. Just made this post to see if I might have something a little off that I could adjust to make maintenance that tiny bit easier 😊 it’s already a breeze using tfp methods though for sure!!
 

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Rumbleehockey03 said:
I meant fill water I assume is 0 since TA stays consistent.
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The fill water TA is probably not zero. Please test the fill water pH and TA to see what they are.
Rumbleehockey03 said:
Ph on 17apr was 7.2. On 28apr it was closer to 6.8 without having added any cya or fill water between that time, and minimal pool usage as well. It’s a slow drift down.
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That just does not happen.

pH does not drop on its own.

Did you get rain?
 
JamesW said:
The fill water TA is probably not zero. Please test the fill water pH and TA to see what they are.

That just does not happen.

pH does not drop on its own.

Did you get rain?
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Tested my fill (top off) water and it’s TA 60 pH 7.5. I think we did get a bit of rain in that period I mentioned earlier...perhaps 1/2” at most. I’ll keep better notes in the coming weeks. Ran a full test today and here’s results:
Water temp: 80
Salt 3400
Cya 70
Ph 7.5
Ta 90
FC 4.5
Cc 0

I’ll keep a good log over the next week of ph, rainfall, and any top off water I add. Again, over the last 2 years I’ve had my pool the ph has always drifted down but mid-summer aeration would keep it steady. Never added acid to this pool before 🤷‍♂️
 
While not the exact same situation, our pool’s pH always drops quite a bit over the winter (Closed, covered, I add nothing over the winter). No one has been able to pinpoint why. Once I bring pH up to normal at opening, it stays rock stable all season without requiring any adjustments.

I do have a couple ideas, though. One, there’s always a ton of dead worms/bugs in the pool at opening. Could all this “organic matter” drop pH? Two, the solid cover does leak a little, so some rain water gets in over the winter. Perhaps the rain here is on the acidic side? I keep meaning to test the rain water to see. ☺️
 
I don't think that even acidic rain could explain that. Your pool is buffered and rain water is pretty unbuffered, adding rain to the pool shouldn't affect the pH directly. The only rain effect is by aeration (rain disturbing the surface) which drives the pH up. It's like that trick to test for pH above FC 10: You can dilute a water sample 1:1 with distilled (!!) water which will half the FC, but hardly affect pH. And your fill water with TA 60 and pH 7.5 also doesn't seem to be the culprit.

The only effect (apart from chlorinating with Tri- or Dichlor) I can think of is chlorine levels going down by a lot. Bleach is pH-neutral as long as you measure pH always at the same point in the chlorination cycle. If you for example brought FC up to 20 ppm, then adjusted pH to 7.2 with MA, and then let the FC come down to 5ppm, your pH might get down to 6.9 or so (ignoring aeration that would happen in parallel). Pretty artificial example, and going down to 6.5 would be really hard, your TA is high enough to make it pretty difficult for pH to drop that low without adding any acids.

Can you list all the chemicals you are adding to your pool, maybe even photos?
 
mgtfp said:
I don't think that even acidic rain could explain that. Your pool is buffered and rain water is pretty unbuffered, adding rain to the pool shouldn't affect the pH directly. The only rain effect is by aeration (rain disturbing the surface) which drives the pH up. It's like that trick to test for pH above FC 10: You can dilute a water sample 1:1 with distilled (!!) water which will half the FC, but hardly affect pH. And your fill water with TA 60 and pH 7.5 also doesn't seem to be the culprit.

The only effect (apart from chlorinating with Tri- or Dichlor) I can think of is chlorine levels going down by a lot. Bleach is pH-neutral as long as you measure pH always at the same point in the chlorination cycle. If you for example brought FC up to 20 ppm, then adjusted pH to 7.2 with MA, and then let the FC come down to 5ppm, your pH might get down to 6.9 or so (ignoring aeration that would happen in parallel). Pretty artificial example, and going down to 6.5 would be really hard, your TA is high enough to make it pretty difficult for pH to drop that low without adding any acids.

Can you list all the chemicals you are adding to your pool, maybe even photos?
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I use a SWG for chlorine, puritech cya, and 20mule team borax to raise ph when needed. Haven’t needed anything else this year.
 

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mgtfp said:
I don't think that even acidic rain could explain that. Your pool is buffered and rain water is pretty unbuffered, adding rain to the pool shouldn't affect the pH directly. The only rain effect is by aeration (rain disturbing the surface) which drives the pH up. It's like that trick to test for pH above FC 10: You can dilute a water sample 1:1 with distilled (!!) water which will half the FC, but hardly affect pH. And your fill water with TA 60 and pH 7.5 also doesn't seem to be the culprit.

The only effect (apart from chlorinating with Tri- or Dichlor) I can think of is chlorine levels going down by a lot. Bleach is pH-neutral as long as you measure pH always at the same point in the chlorination cycle. If you for example brought FC up to 20 ppm, then adjusted pH to 7.2 with MA, and then let the FC come down to 5ppm, your pH might get down to 6.9 or so (ignoring aeration that would happen in parallel). Pretty artificial example, and going down to 6.5 would be really hard, your TA is high enough to make it pretty difficult for pH to drop that low without adding any acids.

Can you list all the chemicals you are adding to your pool, maybe even photos?
Click to expand...
Looking back at test logs, my FC did go from 7 to 9.5 and then down to 6.5 in that timeframe. Not a huge drop, but did go lower.
 

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