Risks with high alkalinity?

[Rangeball]

That's what I thought

However, Bleachcalc threw me off. It has a calc to increase PH by using soda ash, but for borax it only talks about getting to 50 ppm.

Having never had to consider raising PH before, I had never looked at them.

So, that begs the question, how much Borax to raise 21,200 gallons of water .2 ppm?

[Rangeball]

Richard, how was your vacation?

Any idea why my PH would have stabilized at 7.1 with an ALK of 110?

The alk reading is not adjusted for CYA. Should it be? My CYA is about 25.

[chem geek]

Richard, how was your vacation?

Any idea why my PH would have stabilized at 7.1 with an ALK of 110?

The alk reading is not adjusted for CYA. Should it be? My CYA is about 25.

Vacation was great, thanks (a week in Yosemite psuedo-camping at Housekeeping Camp -- it's called Housekeeping for a reason).

I would not normally expect the pH to remain stable at 7.1 with a TA of 110. This is a relative carbon dioxide (CO2) outgas rate of around 28 which is well within the range that people complain about for rising pH (relative rates of 15-20 are when people usually start to complain -- some at 10 in windy areas). So the short answer as to why you found it stable is "I don't know".

And yes, you should quote Total Alkalinity (TA) numbers and not adjust for CYA, but should give the CYA level as well so I can adjust for it. The table and graph I published for CO2 outgassing was for a CYA of 30, but the variation with CYA isn't huge, especially since the rates are relative and actual rates are very dependent on aeration.

Richard

[Rangeball]

Thanks. I'm to the point where I'm considerning adding borax to bring the PH up, but I'm hesitating because my gut is telling me something else may be going on. Also, I may need to add a few inches of fill water in a week or so and that will bring alk up, and most likely PH if history repeats itself.

[Rangeball]

Well, I'm glad I waited.

My daughter had a few friends over a few days ago, really stirred up the water, lot's of diving board action. We've also had a few rains.

I tested PH again last night. 7.8. I couldn't believe it, so I checked again. 7.8. Tested Alk, which was down to 100.

I don't know if the prior batch of kids simply didn't do their job, the rain was enough to keep PH down or some combo of these two, but now I have a problem I've never had before.

What would I have to get my alk down to to get PH to stabilize at 7.5?

I plan to monitor Ph for awhile and see if it drifts up from here.

[chem geek]

I tested PH again last night. 7.8. I couldn't believe it, so I checked again. 7.8. Tested Alk, which was down to 100.

What would I have to get my alk down to to get PH to stabilize at 7.5?

Take a look at the CO2 outgassing chart I made. You were at a pH of 7.1 with a TA of 110 before the kids came over, but as I mentioned, the relative CO2 outgas rate of 28.5 was quite high so I did not expect that to be stable.

Now you had lots of aeration and your pH rose to 7.8. Technically, the alkalinity should not have dropped until you added acid, but ignoring that you are now at a relative CO2 outgas rate of 4.1 which is very stable. In fact, it is surprising that your pH didn't significantly slow down its rise at around 7.5-7.6 so the amount of aeration in your pool must be quite significant (pretty vigorous splashing! maybe some high winds too).

So whereas I initially would have said that you could stabilize around a pH of 7.5-7.6 with your current TA of 100-110, given your significant aeration situation I would say that you would need to get your TA down to around 60-70 to get more stable. Even then, you may still find the pH rise with your kids splashing, but it should rise less and the amount of acid you need to restore the pH should be less. Of course, getting your TA that low with the fill water you have to add may be quite difficult and you may have to live with some intermediate level, but that's up to you.

This rather low TA will make your system bounce a little more in pH from external sources such as adding acid or adding chlorine, but it is still reasonably buffered (it wouldn't be good if you were using Tri-Chlor tablets, for example, due to its acidity, but we all know that Tri-Chlor isn't good for other reasons as well).

Richard

[Rangeball]

Thanks. I plan to leave just monitor it for a few days. Daughter is having the same friends over later this week for a repeat, so assuming the 7.8 holds I may drop PH/alk again before they come and go from there. I'm down about 1.5" on water level, but we've had more rain overnight and again this morning so It may not be as bad now. Plus, the excessive heat has passed, so hopefully evaporation will slow.

On the flip side, school starts in about 2 weeks, and from past experience pool use really slows, so it would be good to get to a stable environment.