Risks with high alkalinity?

[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.

[Rangeball]

After some more rains, PH hit 8. I added acid yesterday, about an hour before some of my daughter's friends were coming over. I had planned to drop ph to 7, but only had enough acid to get to 7.2.

They swam for a good 2 hours, hit the diving board pretty good, lot's of aeration going on. I tested the pool this noon-

PH- 7.2
ALK- 80

This is the lowest I've ever gotten my alk. Richard, with these levels, according to your graph I should now be relatively stable, right?

[chem geek]

Yes, you might still see some pH drift upward, but if it does and you get to a pH of 7.4-7.5 with your TA of 80, then I would expect the drift to slow down to the point it is manageable or maybe even seem to stop. Keep me posted and let me know what happens. If the drift is slower, but still too much to your liking, you can still go a little further down in TA to 70 or even 60 if you like, but I wouldn't go any further down than that. I suspect that 80 will be fine for you, but don't try to keep the pH at 7.2 (7.4-7.5 should be fine) unless is naturally doesn't drift upward anymore.

I'm keeping my fingers crossed for you.

Richard

[Rangeball]

Thanks.

At this point I plan to let it drift wherever it wants. If it settles in below 7.8, I'm fine with that.

I hope it does. This will be a great learning experience for next year, when I can try to get my alk down to 80 or below right off the bat.

Thanks for all your help

[Rangeball]

I planned to add about 2" of water yesterday to make up for evaporative losses.
Started the hose while I was doing some yardwork, completely forgot about it until I came out later to add bleach. Water level was just under the coping, a good bit higher than I wanted to add.

Set valve to waste and brought the level back down so the skimmer would function. Wanted 2" of water, ended up with about 6"+. Will have to test today to assess the ALK damage and start working my way back down...

I am such an idiot.

[Rangeball]

I tested last night.

PH was 7.6
Alk was... no idea. I ran out of reagent after 4 drops...

For what's left of this season, I just plan to monitor PH and knock it down to 7-7.2 every time it hit's 7.8+.

Next year I'll buy more alk reagent, as I use the most of it by far.