Raising pH

[jordangregory]

I am having trouble getting my pH back up here.
I just finished shocking my pool. I have a CYA of 30, TA of 120 (last check about 1 week ago). My FC is at 6 tonight.
2 nights ago I added three pounds of soda ash because my pH was at about 7.
It appeared to stay at 7 when I checked the next day so I added a full 4 lb box of borax.
Checked the pH today and it is at about 7.2.
I thought I would be at about 7.5 according to the pool calculator.
Any thoughts on why things are going up so slowly?

 

[Richard320]

Perhaps your pool holds more water than you think?

 

[JamesW]

The pH might have been below 7. If you shocked with dichlor or trichlor, then the pH would go down. If you have 50 ppm of borates in the water, that will reduce pH rise.

 

[linen]

What ph kit are you using. The taylor drop based kit reads 6.8 for anything below that. Some of the cheaper kits only read 7.0 for everything below that. My guess is your ph might have been quite a bit lower than 7.0 when you started.

As JamesW said, borates will also buffer ph changes.

 

[JamesW]

Any chance that you accidentally used dry acid, instead of pH increaser?

 

[jordangregory]

Thanks for all the responces.
I do believe my pool holds more water than I "thought". The pool calculator defaulted to 10,000 gallons so my calculations were all off!!
I have fixed that.
I do use the taylor drop kit. I never thought that my reading will not go below 6.8. I guess I could have started lower than I thought but it was unreadable. My color coded deal goes from 6.8 to 8.2.
I don't have borates, so I don't think that is the problem.
I shocked with liquid chlorine, so tri and di chlor are not the problem.
I am sure that I did not use dry acid to try and raise up my pH. I used borax.

 

[linen]

I do believe my pool holds more water than I "thought". The pool calculator defaulted to 10,000 gallons so my calculations were all off!!
I have fixed that.

Yep, I think you got it figured out. At 20000, your ph would have gone up ~0.15 with addition of 4 lbs of borax with a TA 120 ppm (according to poolcalculator). Is your pool rectangular and what is the depth(s)?

 

[jordangregory]

Rectangular pool. Shallow end is about 3.5 feet deep and deep end is about 7.5 feet deep.
I have calculated pool size before and I am fairly certain it is 20,000 gallons based on some weird layout features in the deep end.

 

[jordangregory]

Re checked my pH today. pH is back down to 7.2. Two days ago I had it moving up and it was 7.4 ish. What causes pH to trend downwards?
My TA was 120 a few weeks ago when I checked it.

 

[Butterfly]

Anything acidic, like muriatic acid or trichlor.

 

[linen]

Are you using dichlor or trichlor to chlorinate? Both are acidic so your ph would tend to drop.

I would do a fresh TA measurement to see where your at now.

 

[jordangregory]

I am using trichlor in a chlorinator. I guess that means I need either keep working on the pH or try to stick with liquid chlorine if possible

 

[JamesW]

I am using trichlor in a chlorinator. I guess that means I need either keep working on the pH or try to stick with liquid chlorine if possible

Yes, that's one of the issues with trichlor. It's very acidic and will lower the pH and TA. You have to be very careful to monitor the pH to prevent it from going too low.

The other issue is the amount of CYA trichlor adds. For your 20,000 gallon pool, every 7 oz trichlor tab will add 1.5 ppm of CYA.