Water temp effect on PH or PH rise?

[Derb22]

So a little background. I have left the pool open (but now covered with the mesh safety cover because of all the hardwood trees) this winter here in the Atlanta area. In early fall I installed a Stenner Acid pump. I was tired of the weekly 1/2 gallon of acid pours. We swam until late October and the numbers stayed in the perfect range. They were incredibly rock solid. I have been a bit lax in water testing but the other day I ran the numbers and noticed that my PH was down to 7.0 - 7.2. I am assuming that because the SWG wouldn’t and couldn’t produce chlorine now that the water temp is so low and I have taken the swg out of the system that my Normal PH creeping up cycle is now perhaps less. The FC is around 10 which really hasn’t moved and now TA is 50. I dialed back the acid injection time to 1/2 of the daily amount and will go test this weekend again.

One other variable is that I was running the pump 8-10 hours a day during the swim season but now only running it 4 hours per day.

Depending on the responses from the experts about temperature effect and pump time, it does seem that the major contributing factor in my PH rise is directly tied to the operation of the SWG. (No water features at all)

Thanks.

 

[ajw22]

SWG causes bubbles that create aeration and cause PH to rise. Turning down or off your SWG will reduce PH rise.

 

[JamesW]

The main cause of pH rise is high TA.

Warmer water does have an effect because carbon dioxide is less soluble in warmer water.

The next time that you boil a pot of water, notice that bubbles begin to form on the sides and bottom of the pot before the water boils.

That's from dissolved gasses coming out of solution.

Aeration has an effect because it causes the carbon dioxide to come out.

Hot tubs have a problem with rising pH due to the warmer water and aeration causing the carbon dioxide to come out.

A soda or beer also shows both effects as they lose carbon dioxide due to warming up or being agitated.

A SWG has very little to almost no effect on pH rise.

The chemistry of the SWG is completely pH neutral.

As long as the TA is kept low enough, a SWG will not cause pH rise.

 

[Derb22]

A SWG has very little to almost no effect on pH rise.

The chemistry of the SWG is completely pH neutral.

As long as the TA is kept low enough, a SWG will not cause pH rise.[/QUOTE]



James,
Going to have to agree to disagree with your statements. Before SWG installation this spring, Ph was very stable. After installation it starting requiring 1/2 a gallon of MA a week to keep it under 8.0. I even worked hard in getting TA down to 50-60 range with no appreciable slowing of PH rise.

 

[JamesW]

Another source of pH rise is low CSI.

Low CSI causes plaster to dissolve and increases the pH.

What was your CSI during the time that the pH was rising?

One of the biggest reasons for pH problems is due to keeping the pH too low.

This is especially true for people who use acid feeders.

By keeping the pH below 7.8, you create a lot of carbon dioxide, which raises the pH as it offgasses.

All of the added acid lowers the TA too much and you have to add bicarb to raise it back up.

If you kept the pH at 7.8 and the TA at 60, you would get virtually no pH rise.

 

[Derb22]

I will try that this spring. However, there is very little margin of error with 7.8 and it going to 8.0 and higher. The issue with the Taylor test kit is you are clueless to a degree how far over 8.0 you suddenly have gone. I have the TA in the 60 range so will dial in the acid dosage to keep it at 7.8 but I can tell you that without the acid I will go quickly over 8.0.

 

[Derb22]

My csi always runs on the negative side. Around -0.40 / -0.50 on average.

If if I gave you average numbers it looks like this AFTER adding the acid dosing capability.
FC 7.0
CC 0
TA 60
PH 7.6
borates 40
salt 3400
CH 375.
CYA 70

temp in summer runs 78 in May to 85 top end in late August.

 

[JamesW]

The CSI effect on pH rise is strongest when the plaster is new.

Once the plaster cures and carbonates, the effect is reduced.

Keeping the CSI in the -0.3 to 0.0 range will reduce the effect to close to zero.

The bigger issue is that you're keeping the pH too low.

When the pH is below 7.8, a lot of bicarbonate gets turned into carbon dioxide which offgasses and raises the pH.

So, more acid is added, which lowers the pH and TA.

Then, bicarb is added to raise the TA and the cycle continues.

If you keep the pH at 7.8 to 7.9 you will find that the pH will be much more stable.

It's counterintuitive because people think that adding acid prevents pH rise but adding acid actually makes the problem worse.