PH question

[Grinch6]

I have done the pool school. I have searched the forums and gotten what seems like conflicting answers. I have been using the Taylor 2006 or tftkits equivalent for about 12 years now. I take my water to two different pool stores, about every other month to compare. So, I am pretty confident in my numbers. 15K pool. Swg chlorine. FC-2.5, CC - very near zero, CH -375, CYA -60, TA-80, PH-7.2, Salt-3600, Borates-35

So here’s the problem. My SWG runs normally, same as it has since new. I tested the water in the pool and coming out of the chlorinator and found that it was indeed working well. My pool runs 10 hours a day, 7 days a week. Flow is 60gpm. It has bathers in it about 20 hrs a week. It is heated about 2 hours in the am to bring it to 86 degrees. It has 3 waterfalls and two deck jets. They run about 16 hours a week. Chlorine is very stable, slowly varies between 2.2 and 3. The PH keeps going down. A few days ago, I used soda ash to bring it back up to 7.4. Today down to 7.2 again. For years I was adding a little acid regularly to counter the effects of the aeration and the swg. I have not added any in over two weeks and the PH continues to drop. I do shock the pool every other week (based on usage) with 73% cal-hypo. From what I read, I do know the CH effect but poolmath does not show it changes ph. What am I missing?

 

[JamesW]

PH keeps dropping to 7.0

New liner went in 6 months ago along with new coping/pavers. Years ago (2019), I had iron staining problems but ascorbic acid treatments combined with sequestrants and keeping the ph on the lower side (7.2-7.4), solved the problem. Along with a low ph, alkalinity was kept in the 50-70 range to...

www.troublefreepool.com

 

[ajw22]

Is your pool covered when not in use?

 

[Grinch6]

Is your pool covered when not in use?

Yes, always. For this pool, it has been covered when not in use for 7 years. But I am interested in hearing more about covers and ph ph thanks.
Edit: I just read up on off gassing and ph drop with a cover. That makes sense. I just suppose now I need to figure out what I’m doing differently as it has always been covered and I haven’t seen this before while covered. I must have changed something but I am very scheduled and measured with everything I do with the pool. I actually do a drop test for the basics nearly daily.

 

[JamesW]

A cover will prevent loss of carbon dioxide, but that can only reduce pH rise, it cannot cause pH drop.

The first step is to make sure that you don't have a testing error.

The second step is to determine if the pH drop is accompanied by a corresponding TA drop.

 

[ajw22]

Yes, always. For this pool, it has been covered when not in use for 7 years. But I am interested in hearing more about covers and ph, thanks.

The cover keeps the pool from outgassing CO2. The retention of CO2 causes the water to get acidic.

Out gassing of CO2 is the primary reason pH rises in pools. Retain the Co2 with a cover and the water will get acidic.

 

[Grinch6]

The cover keeps the pool from outgassing CO2. The retention of CO2 causes the water to get acidic.

Out gassing of CO2 is the primary reason pH rises in pools. Retain the Co2 with a cover and the water will get acidic.

Thanks, I edited my post above after reading up on off gassing. I have a medically sensitive kid who is the primary user if the pool. I keep the water very balanced for him. My big question now, and likely some more work to be done, is why it is all of a sudden doing this. Its been covered when not in use for 7 years. I track my chemical usage by amount and on a calendar. This is very different than last month and October of last year. I may have found the culprit. See if this makes sense. I changed out my IC40 about a month ago. Is it possible the efficiency of the new one is creating more CO2 that is not dissolved? Still, 7 years, never having to ever add anything to bring the ph up until now. Same cover. Same run times. Same usage.

 

[ajw22]

Show us pictures of your pool and equipment.

 

[JamesW]

Maybe trapped dissolved CO₂ can cause pH drop, but that seems unlikely and it should not cause continuous pH drop.

If there is any drop, I would think that it should stop pretty fast.

X = pH.
Y = %.

The Blue Line is the percentage bicarbonate.

The Yellow Line is the percentage Carbon Dioxide.

H₂O + CO_2aq --> HCO₃^- + H⁺

y = (100/(1+10^(6.35– x))) and y = 100 - (100/(1+10^(6.35– x))), x from 4. to 8. - Wolfram|Alpha

Wolfram|Alpha brings expert-level knowledge and capabilities to the broadest possible range of people—spanning all professions and education levels.

www.wolframalpha.com

 

[ajw22]

I track my chemical usage by amount and on a calendar. This is very different than last month and October of last year.

Can you share that with us?

 

[Grinch6]

Can you share that with us?

Sure thing. I’m working on an ipad right now. it will be later when I get to a computer.

 

[JamesW]

At a pH of 7.73, for every 100 moles of carbon dioxide and bicarbonate, 4 moles will be carbon dioxide and 96 moles will be bicarbonate.

HCO₃^- + H⁺ <--> H₂O + CO_2aq

100 - (100/(1+10^(6.35– 7.73))) - Wolfram|Alpha

Wolfram|Alpha brings expert-level knowledge and capabilities to the broadest possible range of people—spanning all professions and education levels.

www.wolframalpha.com

 

[JoyfulNoise]

You want to track both pH and TA over time. CO2 outgassing will cause a noticeable change in pH with very little change in TA. You'd have to outgas an enormous amount of CO2 to see the bicarbonate levels drop significantly. Chemical additions like muriatic acid or soda ash will often show up very noticeably on pH and TA measurements. So if you start seeing your TA changing with pH, then there's usually some kind of chemical addition causing that. If you see pH changes without any change in TA, those are usually more subtle chemical effects like CO2 outgassing or chlorine reacting with ammonia.

Since you keep your FC very low (pretty much the bottom of the range and holding around the minimum), you should do an overnight chlorine loss test (OCLT) to ensure that you do not have any algae or bacterial growth. Biological contaminations can sometimes cause changes in pH as chlorine oxidation and disinfection reactions often result in acidic by-products.

 

[Grinch6]

Here is a long shot from a neighbor. serratia marescens. Has anyone ever heard of it?

 

[JamesW]

Here is a long shot from a neighbor. serratia marescens. Has anyone ever heard of it?

What is the hypothesis?

 

[Grinch6]

You want to track both pH and TA over time. CO2 outgassing will cause a noticeable change in pH with very little change in TA. You'd have to outgas an enormous amount of CO2 to see the bicarbonate levels drop significantly. Chemical additions like muriatic acid or soda ash will often show up very noticeably on pH and TA measurements. So if you start seeing your TA changing with pH, then there's usually some kind of chemical addition causing that. If you see pH changes without any change in TA, those are usually more subtle chemical effects like CO2 outgassing or chlorine reacting with ammonia.

Since you keep your FC very low (pretty much the bottom of the range and holding around the minimum), you should do an overnight chlorine loss test (OCLT) to ensure that you do not have any algae or bacterial growth. Biological contaminations can sometimes cause changes in pH as chlorine oxidation and disinfection reactions often result in acidic by-products.

My OCLT two nights ago was .6. On poolmath, the suggested chlorine is target of 4, minimum of 2. I keep 2.5 to 3. I will up that.

 

[JoyfulNoise]

Here is a long shot from a neighbor. serratia marescens. Has anyone ever heard of it?

It's a bacteria that can cause uriniary tract infections in humans ... it's also highly susceptible to chlorine disinfection. So no, I sincerely doubt it is the cause of your issues ...

 

[JoyfulNoise]

... and tell your neighbor to stop peeing in pools, it's unhealthy ...

 

[Grinch6]

What is the hypothesis?

I’m in an agricultural and swampy area. Lots of livestock. Lots of swamp decay. Its never been a problem. At the time this all started, we had an EF3 tornado pass a few hundred yards from the house. serratia marscenes is an anaerobic bacteria that comes from animal waste and decay. I called the wife at home and she went and looked closely. All the grout lines do indeed have a light pink tint. She says there are a few nickel size pink dots in the corners as well. I did a quick lookup, and sure enough, thus bacteria gives off CO2 as it begins to ferment in the pool. Now to find out if anything like this has been seen before. New to me. Best I can find is to use 30ppm chlorine. The part that always gets me about stuff like this is when you cannot find anything in 7 years that has changed, yet one day it does. Same chemical balance, same application of chemicals, same temperature, same usage, same cover. All of a sudden you realize that your groundhog days stopped.

 

[Grinch6]

... and tell your neighbor to stop peeing in pools, it's unhealthy ...

My neighbor has the cows. One got tossed up into a tree from the storm. But he does pee outside a lot. I guess that’s a farmer thing