Why am I constantly chasing my pH

[smcurry83]

For the first two months my pool was open, my pH was a constant 7.5. Ever since I added salt and started chlorinating with the SWG, I've been chasing my pH. Every 2-3 days, I find my pH at 7.8-8.0, and add muriatic acid to bring it back down to 7.4. In the beginning I thought it was due to constant heavy rains. But we haven't had any rain in 2 weeks and it's still an issue. It's not my full water either. My well has a pH of 7.5.

I've went through more MA in June than the previous 3 months combined. Including the first 2 weeks to cure my plaster.

All my other chemicals are consistently good, and have been approximately the same since opening Apr 1. pH was stable until I started using the SWG.

FC: 5
CC: 0
TA: 90
CH: 350
CYA: 60
SALT: 3400

What can/should I do to stabilize the pH?

 

[ajw22]

Rising PH is a downside to a SWG.

You can try to lower your TA to 60-70 and see if that helps a bit.

Or you can install an IntelliPH or Stenner Pump to automatically feed your pool the MA.

 

[mknauss]

Have you tested your fill water TA? If you have been adding that much MA and your TA is still at 90, I suspect your fill water TA is elevated.

 

[shingles]

For me, the biggest cause is the SWG. Mine likes to rise as well. It will stick around 8 for a decent time but eventually will push past that. My TA is 60 right now. The rise is slower compared to when it was 70. I might try to push it down to 50 and see if it slows it down more. I may consider a stenner pump at some point to see if I can slow it down. I don’t mind adding but I like to be able to only mess with it every couple of weeks. This way if I and gone for vaca I don’t have to worry about it.

 

[smcurry83]

Have you tested your fill water TA? If you have been adding that much MA and your TA is still at 90, I suspect your fill water TA is elevated.

Fill water TA is ~200. Tested pool TA a few days ago and its holding steady at 90.

 

[mknauss]

With that fill water TA every time you add any to your pool it will push the pH higher. Then your MA adds will slowly erode the TA down and then you add more fill water etc.

 

[smcurry83]

With that fill water TA every time you add any to your pool it will push the pH higher. Then your MA adds will slowly erode the TA down and then you add more fill water etc.

How is that so, if the pH of the fill water is 7.5? I'm not doubting you, I just don't understand the relationship. I'm a pool noob.

I know MA lowers pH and TA. I know aerating will raise pH, but not TA. I had no idea raising TA would also raise pH.

 

[ajw22]

How is that so, if the pH of the fill water is 7.5? I'm not doubting you, I just don't understand the relationship. I'm a pool noob.

I know MA lowers pH and TA. I know aerating will raise pH, but not TA. I had no idea raising TA would also raise pH.

The higher the TA the more rapid your PH will rise when your water is agitated.. And your SWG creates hydrogen bubbles in the water in its cell when it generates the CL.

So high TA was not causing your PH to rise before you had the SWG. Now it is part of the problem.

 

[smcurry83]

The higher the TA the more rapid your PH will rise when your water is agitated.. And your SWG creates hydrogen bubbles in the water in its cell when it generates the CL.

So high TA was not causing your PH to rise before you had the SWG. Now it is part of the problem.

Ok, that makes sense. Its not a rise in TA that's causing a rise in pH. It's a high TA that is allowing for a more unstable pH?

So dropping my TA to 50 or 60 might mitigate some of the instability in pH? And I'll just have to counter the increase in TA when adding fill water, before it has a chance to impact pH?

 

[ajw22]

Ok, that makes sense. Its not a rise in TA that's causing a rise in pH. It's a high TA that is allowing for a more unstable pH?

So dropping my TA to 50 or 60 might mitigate some of the instability in pH? And I'll just have to counter the increase in TA when adding fill water, before it has a chance to impact pH?

TA will constantly be trying to raise PH. It will be be a constant battle. Lowering the TA will just lower the RATE of the rise some.

 

[chiefwej]

You might also look into adding borates to help stabilize the pH.

 

[kicksavedave]

I am having this exact same issue as smcurry83 and my test numbers are nearly identical to his. I had been seeing my PH raise by .6 or .7 over a 4-5 day span, such as when I went away for work for 4 days I got back to an 8.0 reading. Two gals of MA, back down to 7.1/7.2 and then the cycle begins again. TA ranges from 80/90 when the PH is up, and drops to 70 when I lower PH, so its on the same cycle as PH, obviously.

One thing that was most likely NOT causing is is adding fill water, as my cover keeps evaporation to a minimum. I have an autofill, so I can't be certain the exact water fill amount, but my water bill is basically unchanged since before I opened the pool. I suspected it was my new pebble finish still curing and releasing stuff that pushed up the PH, but now I see its more of a common occurance even in well cured pools.

Now what I have recently noticed is, my SWG timing makes an impact. I had it set to 24x7 at 1500 RPM (176 watts) and chlorine set to 25%. That gave me a nice 5.0 FC pretty consistently (CYA 65/70). But in preparation for going solar, and a -time of use- electric plan, I am running the pump at 1650 RPM (206 watts) for 18 hours and the chlorine at 30%. Same total watts, which I get may not equal the same GPM, but should be close. Now my FC has jumped to 8, but my PH has become much more stable, raising by half as much as it used to. I am wondering what all the correlation is here? Slightly faster RPM, a lot more chlorine production, slightly more stable PH. I've already just today lowered the SWG chlorine down to 15% to let my FC drop back to 5.