Low pH and High Alkalinity

Problems relating to pH and total alkalinity.
Increase ph, increase TA. Reduce pH, reduce TA.
pH chemistry advice and techniques for the pool.
duraleigh
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Low pH and High Alkalinity

Postby duraleigh » Mon 30 Aug, 2010 11:01

Ditto what James Watson said above. You would be at risk of damage if you left it over winter.


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Guest

Low pH and High Alkalinity

Postby Guest » Wed 01 Sep, 2010 20:29

I drained the water to about a foot left in the shallow end as I am going to try an dfix the cyranuric acid level. I haeve lots of alage in the pool since the last couple days.

I am having the water trucked in- any advice to get this pool crystal clear again as the new water is being dumped in

I will check all the chemicals tomorrow evening.
Should I dump liquid chlorine in? how many gallons?
James Watson

Low pH and High Alkalinity

Postby James Watson » Wed 01 Sep, 2010 20:56

Get your pH down to about 7.2 and use liquid chlorine to raise the chlorine to about 25 ppm. Maintain 25 ppm until this clears.

You are going to need an FAS-DPD test kit to measure the chlorine at these levels.

If you get a chance, please post a full set of new readings.
James Watson

Low pH and High Alkalinity

Postby James Watson » Wed 01 Sep, 2010 21:00

You can use the pool calculator to calculate how much regular, unscented 6 % bleach or liquid chlorine to add to increase your FC level.
Jimbo

Low pH and High Alkalinity

Postby Jimbo » Sun 05 Sep, 2010 18:30

If you use Tri Chlor tablets and tri chlor shock and have a strong residual at time of testing it could give you a false PH reading so let the chlorine levels fall and retest. Have it tested at the pool store too as the cheaper home test kit solutions are not as accurate. Try using liquid chlorine to shock and tabs to maintain proper chlorine levels though you will need to use acid but this seems to keep total alkalinity more in line over the long run.
James Watson

Low pH and High Alkalinity

Postby James Watson » Sun 05 Sep, 2010 22:46

Jimbo wrote:Try using liquid chlorine to shock and tabs to maintain proper chlorine levels though you will need to use acid but this seems to keep total alkalinity more in line over the long run.

The poster was using tabs. That is what caused their cyanuric acid to go too high in the first place. Tabs would be a bad choice. Also, tabs are acidic, and require the use of pH raising products, not acid.
duraleigh
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Low pH and High Alkalinity

Postby duraleigh » Tue 07 Sep, 2010 07:37

Not to glom on but James Watson has it right. Do NOT use any more tabs!!
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california
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Low pH and High Alkalinity

Postby california » Fri 01 Oct, 2010 19:04

Sounds like I too have been using too much tabs. I went away this summer, left the wife in charge of the pool. I told her to just use the tabs. Algea got outta control so I told her to use more tabs. Cleaned the DE filter when I returned, SUPER SHocked and it cleared up. Couple of weeks later the algea crept back then exploded. Over the last couple of days I have put in 4 gal of liquid Cl, 2.5 lbs of shock 30 oz of algecide. I cleaned the DE filter again, still lots of algea in suspension. I'm really suprised all the CL is used up. Seems like I have added plenty.

I hadn't been checking the ph so
I did that today and found the following:
Total Cl .5
Free Cl 0
pH 6.8
Total Alkalinity 240
Cyanuric Acid 150/300

35,000 gallon pool

I just added 2 gallons Cl. Free Cl has moved to 3 same with the total Cl.

Should I dump another couple of gallons of Cl? The pool looks like lime aid.

How should I balance the alkalinity with the low ph?
chem geek
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Low pH and High Alkalinity

Postby chem geek » Fri 01 Oct, 2010 21:32

I wouldn't worry about the TA if the pH isn't rising too fast. You're going to need to do a significant partial drain/refill to lower the CYA anyway and that will likely lower the TA depending on the TA in your fill water. I suggest you read Defeating Algae, but note that it takes a lot less chlorine for shocking the pool if your CYA is lower and you're going to eventually need to lower it anyway so might as well do that now.

The following are chemical facts that should be disclosed:

For every 10 ppm Free Chlorine (FC) added by Trichlor, it also increases Cyanuric Acid (CYA) by 6 ppm.
For every 10 ppm FC added by Dichlor, it also increases CYA by 9 ppm.
For every 10 ppm FC added by Cal-Hypo, it also increases Calcium Hardness (CH) by at least 7 ppm.

So even with a low 1 ppm FC per day chlorine usage, using Trichlor as the only source of chlorine would raise the CYA by over 100 ppm in just 6 months if there were no water dilution.
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Low pH and High Alkalinity

Postby california » Fri 01 Oct, 2010 21:52

chem geek wrote:...You're going to need to do a significant partial drain/refill to lower the CYA anyway and that will likely lower the TA depending on the TA in your fill water.
The following are chemical facts that should be disclosed:

For every 10 ppm Free Chlorine (FC) added by Trichlor, it also increases Cyanuric Acid (CYA) by 6 ppm.
For every 10 ppm FC added by Dichlor, it also increases CYA by 9 ppm.
For every 10 ppm FC added by Cal-Hypo, it also increases Calcium Hardness (CH) by at least 7 ppm.

So even with a low 1 ppm FC per day chlorine usage, using Trichlor as the only source of chlorine would raise the CYA by over 100 ppm in just 6 months if there were no water dilution.


Yeah, that's gonna be some trick. I don't have a backwash on this pool so I don't know how I'm gonna dump the water. Maybe run the water out the filter with the top of the DE filter removed. then it can hit the deck drains and hopefully make it to the gutter. I haven't done a drain down in the 4 1/2 yars I've had this pool so maybe it is time. I added another gallon of liquid Cl since my last post. Started the sprinkler pool feature.

Yes I belive I have been schooled quite well today on the conditioner build up. Thanks its great info and finally I understand. :thumbup:

I am a little curious about the aeration and how that affects the alkalinity.
anyone care to explain or link me to an explanation?
chem geek
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Low pH and High Alkalinity

Postby chem geek » Fri 01 Oct, 2010 23:53

There is a procedure on lowering TA is here. Aeration is doing anything that will increase air/water exchange such as turning returns up with the pump on high or running a waterfall, spillover or fountain or splashing. It increases the rate at which carbon dioxide leaves the pool. Pools are intentionally over-carbonated to provide a pH buffer and to protect plaster surfaces. Adding acid to water lowers both pH and TA, but the the outgassing of carbon dioxide raises the pH with no change in TA.
James Watson

Low pH and High Alkalinity

Postby James Watson » Fri 01 Oct, 2010 23:55

I am a little curious about the aeration and how that affects the alkalinity.
anyone care to explain or link me to an explanation?


HCO3- + H2O < > H2CO3 + OH- < > CO2(gas) + H2O + OH-

bicarbonate + water < > carbonic acid + hydroxide < > carbon dioxide + water + hydroxide

On the left, you have bicarbonate, which is a component of total alkalinity. On the right, you end up with carbon dioxide and hydroxide (we will ignore the water, as it cancels out).

The hydroxide increases the pH, and it is also a component of total alkalinity. Since one hydroxide ion contributes the same towards total alkalinity as one bicarbonate ion does, the total alkalinity remains the same.

As the carbon dioxide is off gassed by aeration, more bicarbonate ions combines with more water, and the process continues. The net result is an increase in pH with no change in Total Alkalinity. The carbonate alkalinity is decreased, but it is exactly offset by the increase in hydroxide alkalinity.

You list the Cyanuric Acid as "150/300". What is the level, 150 or 300?
James Watson

Low pH and High Alkalinity

Postby James Watson » Sat 02 Oct, 2010 01:16

Also, note that although the hydroxide is a component of total alkalinity, it does not provide any buffering capacity, whereas the bicarbonate does. Adding acid to water with hydroxide alkalinity produces a direct 1 to 1 pH change, whereas adding acid to water containing bicarbonate alkalinity will result in less pH movement.

Therefore, although aeration does not change the TA, it does reduce the TA's buffering capacity.
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Low pH and High Alkalinity

Postby chem geek » Sat 02 Oct, 2010 02:49

Well, it's a little more complicated than that. Unfortunately, the term "buffer capacity" is used in different ways. TA measures the total buffer capacity against a drop in pH in the sense that it measures the amount of pH buffering available all the way down to when the TA test changes color which is at around a pH of 4.5. 25-1/2 fluid ounces of full-strength Muriatic Acid (31.45% Hydrochloric Acid) lowers the TA 10 ppm. When the pH rises from aeration, the TA isn't changed which means that it takes the same amount of acid to get the pH lowered to 4.5 as it did before the aeration. So in this sense, there is still a lot of buffer capacity. It is true that the hydroxyl ions themselves aren't providing that (in practice), but there is very little change in the amount of bicarbonate ion after the aeration -- basically, what mostly happens is that the amount of carbon dioxide in the water is significantly reduced and the shift in pH shifts a little bicarbonate to carbonate and to carbon dioxide (and carbonic acid, which are in equilibrium) which mostly leaves the pool. Some more details about this are in this post and look especially at this post where going from the data listed at pH 7.0 from adding CO2 to the data listed at pH 7.5 is similar to outgassing CO2. The amount of bicarbonate as well as the carbonate alkalinity hardly changes, but the Total Carbonate (which includes carbon dioxide and carbonic acid) does change -- basically, it is the concentration of CO2(aq) that is mostly changing (in absolute, not percentage, amounts).

Another measure of buffer capacity is the resistance to an incremental change as expressed in millimoles/pH (for 1 liter so really it's millimoles/liter/pH). This measure drops dramatically for the bicarbonate buffer system (technically, the bicarbonate / carbonic acid system) as the pH rises, but it's not really due to hydroxyl being weaker as much as it has to do with the pH moving further away from the pKa of that system (around 6.3). If one has 50 ppm Borates in the water, then the borate buffer system gets stronger as the pH rises since the pH is getting closer to the pKa in this case (around 9.1).
california
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Low pH and High Alkalinity

Postby california » Sat 02 Oct, 2010 11:59

James Watson wrote:
You list the Cyanuric Acid as "150/300". What is the level, 150 or 300?


Visually on the test strip it looked between the 2 values. I am going to try the dilution test, 4 parts tap water to 1 part pool water. I'll let ya know what that reads.
With a 4 to 1 dilution the alkalinity still reads above the 180 comparison on the test strip. Multipling that by 5 and well, That's a high alkalinity. The cyanuric read a respectable 30-50. Multipling that and I lose my respect and have 150 to 250 ppm.
I tested again with a sample of straight pool water (harvested a foot under the surface) and the CyA and alkalinity was off the chart. Funny thing, there seems to be more free Cl in the tap water than in the pool

I have never backwashed or drained any significant part of the pool in 4 1/2 years, just topped up with local water. For the most part I have just used tablets, shock packets and the occasional liquid for a quick boost the Cl. This past year, I have gone through a half dozen bottles of algeacide. Prior years, I used maybe one or two.

From what I have been reading, I think I need to dump some pool water so I can dilute my alkalinity and cyanuric level. But how much do I need to dump? Is the water unsafe for the lawn?

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