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Added 1/2 Gal Of Acid And Ph Dropped To 7.2!


Gavin

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every week I've been adding 1/4 gal acid to try and drop the pH down to 7.4-7.6 but it didn't want to budge.

some info:

pool size: 10,100 gallons

pool type: gunite

FC: 7 (added 1 gal of 10% bleach today 4hrs after adding the acid)

pH: was 7.8

TA: 120

CYA: like 120-150 (I need CYA tester that goes that high but thats an approx)

so today I added 1/2 gallon of muriatic acid and tested 4 hrs later and the pH is now 7.2

just wondering why it didn't budge from 7.8 when I was adding 1/4 gallon and now I add 1/2 gallon and it drops too low!?? :unsure:

should I be measuring in fluid ounces? do I used the acid demand test and some sort of measuring cup?

help please. I don't want plaster damage. Thanks! :(

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Assuming you Muriatic Acid is full-strength (31.45% Hydrochloric Acid), then 1/4 gallon in 10,100 gallons would lower the TA by about [EDIT] 12.5 ppm [END-EDIT] so I suspect that your TA was very high before and your pH wasn't dropping because a high TA outgasses carbon dioxide faster and that causes the pH to rise. So the net effect of your first acid additions was to lower the TA. As the TA got lower, additional acid will show up as a pH drop as well because there will be less carbon dioxide outgassing so less pH rise.

Have you been adding either pH Up or Alkalinity Up in the past?

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Assuming you Muriatic Acid is full-strength (31.45% Hydrochloric Acid), then 1/4 gallon in 10,100 gallons would lower the TA by about 25 ppm so I suspect that your TA was very high before and your pH wasn't dropping because a high TA outgasses carbon dioxide faster and that causes the pH to rise. So the net effect of your first acid additions was to lower the TA. As the TA got lower, additional acid will show up as a pH drop as well because there will be less carbon dioxide outgassing so less pH rise.

Have you been adding either pH Up or Alkalinity Up in the past?

Thanks Chem geek. No just adding acid and bleach. I usually add the acid first and then wait 30mins before adding the bleach.

So hopefully now the TA might go down a bit more and the pH raise slower? the TA was 120 and pH was 7.8 then I added 1/2 gal of acid. 4hrs later I tested the pH again and it was down to 7.2....I then added 1 gal bleach (10% bleach). FC was 7 but CYA was 120-150 approx.

you are right last week TA was 140 then I added 1/4 gal acid so 120 sounds about right. I hope I didn't lower the TA too low? :(

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Also, if you have a lot of scale or plaster dust from new plaster, that creates an unmeasurable level of alkalinity in addition to your measurable alkalinity. The acid will dissolve the scale or plaster dust, and once the scale or dust is gone, the pH will suddenly drop more than expected.

Your high cyanuric acid will also contribute to your total alkalinity. If your cyanuric acid is 150, then it will contribute 50 ppm to your total alkalinity.

As Richard noted, carbon dioxide outgasses faster at higher levels of alkalinity. It is the carbonate portion of the alkalinity that determines the rate of carbon dioxide outgassing.

If your Total Alkalinity was originally 170 a few weeks ago, the carbonate portion would have been 120. Now that the Total Alkalinity is 120, the carbonate portion is 70.

The rate of carbon dioxide outgassing slows as you begin to approach the water's natural equilibrium level of carbon dioxide. Knowing the carbonate portion helps better determine the effect of adding acid on pH. The pH also has farther to come back from adding 1/2 gallon as opposed to 1/4 gallon because you bring it to a lower level. It will take more time to recover.

You can get a more accurate measurement of your cyanuric acid by diluting the sample and multiplying by the dilution factor.

Mix 1 part pool water and 2 parts tap water and then test the diluted sample. Multiply the result by 3 to get your result.

How long ago was the plaster completed?

What is your calcium level?

What is your more accurate cyanuric acid level?

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Also, if you have a lot of scale or plaster dust from new plaster, that creates an unmeasurable level of alkalinity in addition to your measurable alkalinity. The acid will dissolve the scale or plaster dust, and once the scale or dust is gone, the pH will suddenly drop more than expected.

Your high cyanuric acid will also contribute to your total alkalinity. If your cyanuric acid is 150, then it will contribute 50 ppm to your total alkalinity.

As Richard noted, carbon dioxide outgasses faster at higher levels of alkalinity. It is the carbonate portion of the alkalinity that determines the rate of carbon dioxide outgassing.

If your Total Alkalinity was originally 170 a few weeks ago, the carbonate portion would have been 120. Now that the Total Alkalinity is 120, the carbonate portion is 70.

The rate of carbon dioxide outgassing slows as you begin to approach the water's natural equilibrium level of carbon dioxide. Knowing the carbonate portion helps better determine the effect of adding acid on pH. The pH also has farther to come back from adding 1/2 gallon as opposed to 1/4 gallon because you bring it to a lower level. It will take more time to recover.

You can get a more accurate measurement of your cyanuric acid by diluting the sample and multiplying by the dilution factor.

Mix 1 part pool water and 2 parts tap water and then test the diluted sample. Multiply the result by 3 to get your result.

How long ago was the plaster completed?

What is your calcium level?

What is your more accurate cyanuric acid level?

wow thanks I didn't know all that. I also thought having a high TA it would keep pH more in check. should I add some baking soda?

ch - 1200

plaster is 5yrs old and there is some plaster coming off in a couple places.

I will try that and retest the cya. thanks!

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Your Calcium Hardness is 1200? Is that correct? How did you test that?

It is important to know that there is a measurement for Calcium Hardness and a measurement for Total Hardness, which includes other hardness, like magnesium. Test strips measure Total Hardness. You need a drop test kit to test for Calcium Hardness.

A high Carbonate Alkalinity will cause your pH to increase. You need to get the Carbonate Alkalinity where it will keep your pH stable.

What are your current levels of:

pH

Total Alkalinity

Cyanurate Alkalinity

Carbonate Alkalinity

Calcium Hardness

Cyanuric acid

Temperature

CSI

Cyanurate alkalinity = 1/3 of the Cyanuric Acid level.

Carbonate Alkalinity = Total Alkalinity- Cyanurate Alkalinity

CSI = Calcite Saturation Index

You can use the thepoolcalculator.com to determine your CSI. Be sure to fill in ALL of the information.

When using the Taylor Watergram slide rule calculator, you need to use the Carbonate Alkalinity to get the correct CSI. If it is a salt-water pool, you have to subtract 0.2 from the number.

If you use the Taylor electronic Watergram Water

Balance Calculator, it will take calculate the correct number when you add the cyanuric acid level and the Salt level (TDS or DS = Total Dissolved Solids).

The thepoolcalculator.com is the most accurate and will also include borate levels in the calculation.

Also, is this the painted pool that you referenced in another post?

Another thing to consider is that you might not be getting a correct calcium reading if you have metals, such as copper, in the water. Metal ions can interfere with the calcium test.

To prevent this interference, add 10 drops of reagent number R-0012 and swirl to mix before adding the 20 drops of reagent R-0010. Then add 5 drops of R-0011L. Then add the R-0012 drop by drop until the solution changes from red to blue. Add the original 10 drops of R-0012 to the number of drops of R-0012 added to get the color change for the total number of drops of R-0012.

What is the Calcium Hardness of your fill water?

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Your Calcium Hardness is 1200? Is that correct? How did you test that?

It is important to know that there is a measurement for Calcium Hardness and a measurement for Total Hardness, which includes other hardness, like magnesium. Test strips measure Total Hardness. You need a drop test kit to test for Calcium Hardness.

A high Carbonate Alkalinity will cause your pH to increase. You need to get the Carbonate Alkalinity where it will keep your pH stable.

What are your current levels of:

pH

Total Alkalinity

Cyanurate Alkalinity

Carbonate Alkalinity

Calcium Hardness

Cyanuric acid

Temperature

CSI

Cyanurate alkalinity = 1/3 of the Cyanuric Acid level.

Carbonate Alkalinity = Total Alkalinity- Cyanurate Alkalinity

CSI = Calcite Saturation Index

You can use the thepoolcalculator.com to determine your CSI. Be sure to fill in ALL of the information.

When using the Taylor Watergram slide rule calculator, you need to use the Carbonate Alkalinity to get the correct CSI. If it is a salt-water pool, you have to subtract 0.2 from the number.

If you use the Taylor electronic Watergram Water

Balance Calculator, it will take calculate the correct number when you add the cyanuric acid level and the Salt level (TDS or DS = Total Dissolved Solids).

The thepoolcalculator.com is the most accurate and will also include borate levels in the calculation.

Also, is this the painted pool that you referenced in another post?

Another thing to consider is that you might not be getting a correct calcium reading if you have metals, such as copper, in the water. Metal ions can interfere with the calcium test.

To prevent this interference, add 10 drops of reagent number R-0012 and swirl to mix before adding the 20 drops of reagent R-0010. Then add 5 drops of R-0011L. Then add the R-0012 drop by drop until the solution changes from red to blue. Add the original 10 drops of R-0012 to the number of drops of R-0012 added to get the color change for the total number of drops of R-0012.

What is the Calcium Hardness of your fill water?

Thanks for the reply.

I have a Taylor K2006

This is a friends pool.

some readings...

pH: 7.2

Total Alkalinity: was 120 will need to test again

Cyanurate Alkalinity

Carbonate Alkalinity

Calcium Hardness: 1200

Cyanuric acid: 120-150 (I need a test tube that goes above what the Taylor K2006 has)

Temperature: (I don't know. I've been meaning to get a thermometer)

CSI: (I'm unable to test for salt or temperature so haven't worked it out)

I can see I really need a thermometer and a better CYA test kit to work out the CYA Alk and Carbonate Alk, CYA and CSI. I need to go to the pool shop.

I haven't tested the fill water. I really should do that. Thanks.

Can I use test strips to test for copper and iron? would they be accurate enough? I don't think i can get the drop test kits in my area.

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I don't know that there is a "better" CYA kit; a CYA as high as yours is usually considered a real problem. You can double the range of the K2006 test by diluting your sample half-and-half with tap water; test CYA of that mix, then double the result.

--paulr

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I don't know that there is a "better" CYA kit; a CYA as high as yours is usually considered a real problem. You can double the range of the K2006 test by diluting your sample half-and-half with tap water; test CYA of that mix, then double the result.

--paulr

Yes thanks I think that would be the better solution. i did see a CYA test in the pool store. The tube might go higher than the one in the K2006 kit but I like the idea of doing the half and half with tap water. B)

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I know of no CYA test that goes higher than 100 ppm (except perhaps a turbidity meter). There are some tests that will go lower than 30 ppm. For example, the Taylor K-1720 or the tftestkits.net Cyanuric Acid test.

When your CYA is very high, then as you say you can dilute with tap water to get a reasonable estimate that is in the <100 ppm range and there is nothing wrong with doing that.

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I know of no CYA test that goes higher than 100 ppm (except perhaps a turbidity meter). There are some tests that will go lower than 30 ppm. For example, the Taylor K-1720 or the tftestkits.net Cyanuric Acid test.

When your CYA is very high, then as you say you can dilute with tap water to get a reasonable estimate that is in the <100 ppm range and there is nothing wrong with doing that.

sounds good. that will save me some money. thanks. B)

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