Borate buffering and high pH?

[prs]

I discovered TFP about six months ago when in the process of draining the pool and having 12 years of Calcium buildup blasted off the tile. I've been using the TFP method ever since to great effect....thank you TFP !!!

The TFP recommended pH is 7.5-7.8 and every week when I do my tests I find pH has risen to 7.8, so I add enough MA, from PoolMath, to take it back to 7.5. I added 25 lbs of boric acid in April to bring my borates level to 25ppm and when that didn't stop the pH increase I added another 25 lbs in June, but again every week ph had risen to 7.8. TA has been rock steady at 70 all this time.

A couple of weeks ago I looked at my log and realised that with no borates I had been adding 14 ozs of acid per week, with 25ppm borates I had been adding 29 ozs per week, and now at 50ppm I'm adding 43 ozs per week. So all the borates had done for me was increase acid use by 30 ozs per week. !!!

After thinking about it I figured that didn't make any sense, so I didn't add any acid last week...this week I tested again and my pH was still at 7.8. It looks like the borates buffering effect in my pool occurs at pH 7.8. So my inclination is to continue not adding acid and see how long I can go at 7.8. My worry is that I've read plenty of threads were people have pH lower than 7.5 but I've never seen anyone with ph higher than 7.8.

So if my ph goes up to 8.0 or 8.2 is that a big problem?

PS. At 73°F water temp and pH of 7.8 my CSI calculates out to -0.35, and at ph 8.2 it would be -0.27, so that looks pretty good.

 

[Killer95Stang]

Funny... I am in the same boat as you. Because of high CH levels from fill water I always kept my pH between 7.2 and 7.5. After adding 40 ppm of borates, my pool loves to rise quickly to a range between 7.5 and 7.8. I am now using three times the amount of acid to get me back down to 7.2. I love the borates, but I'm not seeing the as much of the buffering effects that I thought I was supposed to see.

 

[pwrstrk]

Funny... I am in the same boat as you. Because of high CH levels from fill water I always kept my pH between 7.2 and 7.5. After adding 40 ppm of borates, my pool loves to rise quickly to a range between 7.5 and 7.8. I am now using three times the amount of acid to get me back down to 7.2. I love the borates, but I'm not seeing the as much of the buffering effects that I thought I was supposed to see.

What's your TA level ?
I think, somebody correct me if I'm wrong, that the addition of borates will increase the amount of acid needed to lower PH. ?

 

[chem geek]

What would happen after adding borates is that it shouldn't change the amount of acid you add over time but rather would reduce the frequency of that acid addition, so you'd add a larger amount of acid each time, but spaced out longer in between additions. With borates, it takes more acid to lower the pH from 7.8 to 7.5, but it should take longer for the pH to go from 7.5 up to 7.8 such that the amount of acid over time should be the same. That's not what you saw and I don't have an explanation for that.

It is true that the pH buffering from the borates is stronger at higher pH so the pH stability will seem better at 7.8 than at 7.5, but you'd still have to add acid at 7.8 to keep it there. If you find that it's stable at 7.8, then that would likely have happened without the borates as well. I suspect that your pH isn't actually stable at 7.8 but the borates will have it be longer before you see the pH go up from 7.8, but when you do try and lower the pH back to 7.8 it will take more acid to do so than without borates.

 

[prs]

Thanks chem geek. I'm not going to add any more acid for now and test pH every couple of days. Maybe I'll find the ph stabilizes at 7.8 or slightly higher.

If the pH drifts up to 8.0 or 8.2 is that a problem? Is that high a ph OK for bathers?

 

[JasonLion]

High PH can potentially cause calcium scaling and/or metal staining. Neither of those are certain to happen, depending on other factors. The risk increases as the PH increases, so going over a little is only a tiny risk, while going over a lot is a larger risk.

 

[Kiss4aFrog]

I would think it would be a problem for a number of reasons with swimmers having irritated eyes and likely itchy and sticky skin being the most important.
Other problems:
High pH can cause a hazy, murky, or cloudy pool, making the pool not very inviting.
Over time, high pH can cause water to scale, resulting in filters and fittings plugging, and pipes gaining scale on the inside.

 

[chiefwej]

Wouldn't a lower TA allow the pH to balance a bit lower? I've found that if I keep my TA level from getting too high the pH seems more stable.

 

[prs]

Chiefwej, my TA is at 70 now, I don't know if lowering it to 60 would help, but I just put that number in PoolMath and it takes my CSI from -0.35 to -0.51 so probably best not to try it.

I do wonder what happens to all the extra acid. Is it possible it's just hanging out there at pH 7.8 and doesn't get used up until the pH increases to 7.8? If that's the case it should be about three weeks from the last acid add before the pH goes above 7.8. I'll keep testing and check it out.

 

[chem geek]

I would think it would be a problem for a number of reasons with swimmers having irritated eyes and likely itchy and sticky skin being the most important.

As noted in this paper eye irritation is associated with a low salt level and with chloramines, but not with chlorine level nor with pH (from 7.0 to 8.8).

Acid addition will lower both pH and TA while carbon dioxide outgassing will raise the pH with no change in TA. So with acid addition you should see the TA slowly drop over time unless you've got some other source for TA rise such as plaster curing or water evaporation and refill.

 

[prs]

Three weeks since my last acid add and pH has crept up to 7.9. I'll hold off on acid and keep checking

Borates obviously effects ph at the acid add, 43 ozs MA always took my pH down from 7.8 to 7.4-7.5, PoolMath says that with no borates 43 ozs would have taken pH down to 7.1. It does seem reasonable to assume that if borates effects pH on the way down, it will have some effect on the way back up. Chem geek suggests my pool might have stabilized at 7.8 with no borates but I suspect not. I checked my acid log and it shows three or four weekly pH test results of 8.0 before I added any borates, and the ph had been taken down to 7.5 the week before.

Pool School is pretty definite that the acceptable pH range is 7.5 to 7.8 so I suspect that, like me, many TFP followers add acid as soon as they get a pH test result of 7.8. If borates buffering can cause pH to stabilize at 7.8 then this might be worth a mention in the Chemistry 201 Borates sticky thread. Letting people know their pH might be buffered for weeks at a time at the high end of the range could save them from wasting a lot of acid.

 

[JasonLion]

The PH stability question is far more complex than what you describe, and has very little to do with borates. Simplifying greatly, PH is more stable when PH is high, TA is low, and aeration is low. Borates change the rate at which PH changes, but not where it stabilizes. If you are having problems with PH going up rapidly your best bet is usually to lower the TA, as that is the easiest factor for you to change.

For most pools most of the time, I would wait until the PH goes above 7.8 before lowering it. 7.8 is a perfectly fine PH.

 

[chem geek]

Yes, the borates just slow down the RATE of rise, but you still need to add the same amount of acid as before -- just less frequently. When I said it may settle in at 7.8, I didn't mean it would necessarily stop rising completely, but rather slow down to the point where that was a reasonable target to maintain.

Technically, the pH will only stop rising from carbon dioxide outgassing at a rather high pH depending on TA level and except for very low TA that pH is over 8.0. It's just that the rate slows down significantly before then so in practice feels like it settles in even though technically it may still be rising.

Also, there are other sources of pH rise other than carbon dioxide outgassing and those won't slow down from a lower TA or higher pH target. Such sources would be plaster curing (or degrading) and undissolved chlorine gas outgassing from an SWCG (usually when one has short pipe runs).

 

[prs]

Chem geek, thanks for helping me out on this, I think we are saying the same thing. The only point I'm trying to make is that the reduced rate of pH rise with borates does not seem to be uniform over the pH range. My pool ph rises from 7.5 to 7.8 in a week with or without borates. However with no borates the pH keeps on rising past 7.8, but with 50ppm borates the pH holds steady at 7.8 for another two weeks.