pH balancing

[run53]

I opened my pool this weekend and found that my pH was on the high side (7.8 - 8.0). My TA was 60 and my CYA was 20-30.

So I added 2 cups of MA (22K gallon pool). I was hoping that would bring down the pH to 7.4 or so based on the Pool Calculator. I also started to add CYA through a nylon stocking, hoping to get that up to 70-80 for my SWG pool (about 8-9 lbs.).

However when I remeasured pH this morning, it was 6.8 - 7.0 and my TA was 50-55 (went down a little). I know that my pH will rise due to the SWG but I think it's too low and want to get it at least into the 7.2-7.4 range. I've never had to raise pH in my pool before so I am wondering the best way to do it. Should I use Borax or Sodium Carbonate? I think it should be Sodium Carbonate, since the TA is a little low and that will tend to raise the TA more than Borax. However, I've had negative experiences with Sodium Carbonate in my Spa (stand alone) as it has turned my water cloudy (usually clears in a week or so).

So my questions are...should I even bother to raise the pH, since my SWG will naturally raise it over time (I could also aerate more) ? And if I raise it, should I be using Borax or Sodium Carbonate (washing soda).

Thanks in advance for any comments you may have......this place has bailed me out on a number of occasions!

 

[JasonLion]

Yes, you should raise the PH, but only just a little, to about 7.2, and then let it come up the rest of the way on it's own. Sodium carbonate (soda ash, washing soda) is fine. It will raise both the PH and TA, which is good right at the moment. You could instead add a little baking soda to bring TA up to about 70 and then see where the PH is and use borax to raise the PH.

Anything which raises PH runs some risk of causing clouding when some combination of PH, TA, and CH levels are high. Given how low your PH is, there shouldn't be any risk of clouding right at the moment.

 

[run53]

Yes, you should raise the PH, but only just a little, to about 7.2, and then let it come up the rest of the way on it's own. Sodium carbonate (soda ash, washing soda) is fine. It will raise both the PH and TA, which is good right at the moment. You could instead add a little baking soda to bring TA up to about 70 and then see where the PH is and use borax to raise the PH.

Anything which raises PH runs some risk of causing clouding when some combination of PH, TA, and CH levels are high. Given how low your PH is, there shouldn't be any risk of clouding right at the moment.

Thanks...I like the baking soda idea, since my TA is a little low anyways. It might also raise my pH to the low 7's.

 

[Puffin]

Why do you think you were off? Any ideas? Did the CYA have that large and effect on your PH?

 

[run53]

Why do you think you were off? Any ideas? Did the CYA have that large and effect on your PH?

That's a good question......not sure what effects low CYA might have on pH.

If anyone has any thoughts on this, please chime in.

 

[JasonLion]

CYA typically only lowers PH by about 0.1 or maybe 0.2, though it can lower PH more when the TA level is low, as it is here.

It is also tricky to get quantities for PH changes exactly right because there are so many possible sources of error (pool size, TA measurement, PH measurement, borate level, etc).

 

[chem geek]

Actually, CYA lowers the pH by quite a lot if you adding a lot of CYA. Adding 50 ppm CYA to a pool with 80 ppm TA will lower the pH from 7.5 to 7.0 while in a pool with 50 ppm TA it will lower the pH from 7.5 to around 6.9. In practice, when the pH gets lower, carbon dioxide outgassing increases so you may not see the full pH drop. One pound of CYA is equivalent to adding roughly 10 fluid ounces of full-strength Muriatic Acid (31.45% Hydrochloric Acid) in terms of its effect on pH (the actual amount varies somewhat depending on the starting pH since CYA is a weak acid).

In my own pool, I've added smaller amounts of CYA -- roughly 20 ppm -- and still noticed a pH drop from 7.5 to around 7.2.

 

[run53]

Actually, CYA lowers the pH by quite a lot if you adding a lot of CYA. Adding 50 ppm CYA to a pool with 80 ppm TA will lower the pH from 7.5 to 7.0 while in a pool with 50 ppm TA it will lower the pH from 7.5 to around 6.9. In practice, when the pH gets lower, carbon dioxide outgassing increases so you may not see the full pH drop. One pound of CYA is equivalent to adding roughly 10 fluid ounces of full-strength Muriatic Acid (31.45% Hydrochloric Acid) in terms of its effect on pH (the actual amount varies somewhat depending on the starting pH since CYA is a weak acid).

In my own pool, I've added smaller amounts of CYA -- roughly 20 ppm -- and still noticed a pH drop from 7.5 to around 7.2.

Well, this explains what happened then. I added about 4 lbs of CYA along with 16 oz MA. I've noticed my pH slowly rising each day though.