PH too low for how long to cause problems?

[shoot_the_goalie]

Hypothetically, how long would low pH need to be at to be corrosive?

my pH rises steadily every day, being a relatively new SWCG pool. (about .1 pH a day). So I typically need to add a quart or so about 1-2 times a week to keep my pH around 7.6-7.8.

Say I went away for a little bit and didn’t want my pH to rise too high. Would it be okay to drop the pH around 6.8 for a few days and let it slowly rise on its own so that when I returned the pH wouldn’t be too high? I know low pH can be corrosive...but would that take days, weeks in order to cause any problems?

 

[YippeeSkippy]

Well, lets first consider- what's causing this rise in pH all the time?
-Is this a new pool??? Plaster still curing??
-Are you running water features such as fountains that cause pH rise.

If its a new pool, it has to cure. Part of that process is bumping down the pH as it naturally rises in the curing process. This can take months.

If you're running features that make lots of surface bubbles (which raise pH), can you cut those down to minimal use daily and see if that helps?

We would like a full set of test results to see too, particularly your TA-
FC
CC
pH
TA
CH
CYA

We might want to tweak that TA down to slow your pH rise.

And to answer your original question.... I dunno how long it takes? It just *does* for some.
Maddie

 

[shoot_the_goalie]

FC: 5.5-6.0
CC: 0.0
pH: 7.6
TA: 70
CH: 375
CYA: 70
Salt: 3800
Temp: 84

Using TFKIT100

Happy with my water chemistry. Just wondering it it’s ok to drop my pH to like 6.8 if I go away for like a week or, so that when I get back it’s not over 8.0. Like I said, my pH tends to rise about 0.1 a day. Pool a year old, SWCG runs 24/7 at 20%, no water features that aerate. I’m just curious if it takes like days or weeks at low pH to cause corrosion. I’d imagine, knowing my pool, that it would only be in the under 7.2 range for like 3-4 days and this would only be done occasionally. Thanks.

 

[JamesW]

FC: 5.5-6.0
CC: 0.0
pH: 7.6
TA: 70
CH: 375
CYA: 70
Salt: 3800
Temp: 84

Using TFKIT100

Happy with my water chemistry. Just wondering it it’s ok to drop my pH to like 6.8 if I go away for like a week or, so that when I get back it’s not over 8.0. Like I said, my pH tends to rise about 0.1 a day. Pool a year old, SWCG runs 24/7 at 20%, no water features that aerate. I’m just curious if it takes like days or weeks at low pH to cause corrosion. I’d imagine, knowing my pool, that it would only be in the under 7.2 range for like 3-4 days and this would only be done occasionally. Thanks.

It doesn't work like that. Lower pH rises much faster than higher pH because it creates a lot more carbon dioxide.

It also lowers the CSI, which dissolves the plaster a little bit and causes ph rise from the calcium carbonate in the plaster cement.

The best thing to do is keep the pH at 7.8 and the CSI at -0.3 to 0.0.

 

[skimmerswimmer]

I believe pebble and hydrazzo finishes can handle a lower PH better than regular plaster, but you also have to consider your heater when lowering PH. During my pebble fina cure, I tried to keep my PH at around 7.0 for many months due to some uneven mottling that I was trying to address for the first year or two. If you can bypass your heater, then I would say a short term PH of 6.8, rising to your normal PH after a week or two would most likely not be much of a risk to your finish. Hot starts have much lower PH than that, but they usually have their own pumps to circulate the water and the heater and the rest of the system is kept off line.

 

[JamesW]

Dropping the pH that much would also lower the TA. It really won't work. The pH rise is exponential with lower pH rising much faster than higher pH.

A certain percentage of the bicarbonate will convert to carbon dioxide depending on the pH.

pH........%CO2
4.5.......100.0
6.3.........50.0
7.2........ 11.2
7.3......... 9.1
7.4......... 7.4
7.5......... 5.9
7.6......... 4.8
7.7......... 3.8
7.8......... 3.0

So, the TA x the percentage determines how much carbon dioxide is in the water.

A lower pH causes more carbon dioxide and has higher pH rise.

For example, a TA of 120 and a pH of 7.4 will have about 4.9 times as much carbon dioxide as a TA of 60 and a pH of 7.8.

So, the pH rise will be about 5 times as much.

Even at the same TA, the amount of carbon dioxide is about 3.7 times higher at a pH of 7.2 vs 7.8.