Raise Ta And Lower Ph

[ThomasSE]

Hi, been lurking around this forum trying to get an answer to my problem...

I have read Nitros excellent guides but I still want to get learn more.

I refilled my tub a week ago. After filling I first adjusted the TA level to 100. Then the CH to 150. Everything fine there, but my PH was waaay too high, 8.5. (My tapwater has ph 8.5)

So, I used PH-down and got the ph down to 7,6. But then TA got down to 50-60...

Filled with more baking soda to get back TA to 100.. but then PH is also increased to 8.3.

I've read in several places that this is normal and that ph is more important than TA? So I should accept lower TA as long as the ph is good?

Sorry is this topic has been covered in a previous thread...

Edit: It has, found it. Wonder how I missed this one

http://www.poolspaforum.com/forum/index.php?showtopic=23132

//Thomas

[chem geek]

Yes, as you found, TA is a SOURCE of rising pH itself (due to faster carbon dioxide outgassing) so having a lower TA makes the water more stable against a rise in pH so leave the TA at 50-60 and perhaps use 7.6 or 7.7 as your pH target if that is where it tends to be stable. You can also add 50 ppm Borates to the water for additional pH buffering that doesn't lead to outgassing of carbon dioxide.

[ThomasSE]

Yes, as you found, TA is a SOURCE of rising pH itself (due to faster carbon dioxide outgassing) so having a lower TA makes the water more stable against a rise in pH so leave the TA at 50-60 and perhaps use 7.6 or 7.7 as your pH target if that is where it tends to be stable. You can also add 50 ppm Borates to the water for additional pH buffering that doesn't lead to outgassing of carbon dioxide.

Strange is that the manufacturer of the SPA wants me to have 100-150 TA and 7.4-7.6 ph. Seems impossible with the chems I got with the tub.

//Thomas

[NewB@Spa]

Yeah don't you love how the manufacturers and pool stores all send you in a death spiral trying to get the balance right. I just did a fill and my TA is ~ 80 and my Ph is about 8.1

I am going to add more Ph down this afternoon and remeasure both Ph and TA. I expect TA to lower to about 60-70 which I can live with as long as my Ph stays stable. When I added the Borates (Boric acid) I only added ~8oz because I figured I could always add more later. Chem Geek do you recommend adding the remaining 8oz of Boric Acid?

I am still in the adding Dichlor stage so I can get my CYA to ~25 (measured, not calculated) then switch to bleach.

[kbaumann]

Can we not add the Boric Acid all at once to get the 50ppm borates?

Here was my plan to cleaning & refilling the spa (Not like Nitros?)

1) Add spa flush and then return the next day.

2) Drain & fill the spa using metal filters.

3) Add the Boric Acid to get the 50ppm borates.

4) Add liquid conditioner to get the 30ppm CYA (Not Dichlor).

5) Test the TA and adjust.

6) Test the CH and adjust.

7) Shock the spa with bleach to 12-14ppm.

8) Turn the temp up to 100F-106F

9) Return next day to recheck all chems.

In that order.... hmmmmmm Anything wrong?

[NewB@Spa]

I am going to be very interested to hear the experts weigh in on this one. I had exactly the same idea, although I did not follow through. I opted to stick to Nitro's regimen (I am on day 4) Balanced the 1st day, calculated CD on day 2 and soaked that night. Added Dichlor to get to 10 ppm (probably should have put less in) Soaked again last night and added 3ppm (.5oz Dichlor). Just measured FC (using DPD test) and measured 3.5. Again I added enough to take it to 6ppm (.33oz)

[chem geek]

One can add the 50 ppm Borates all at once. Adding less just has less pH buffering.

One can use Instant Pool Water Conditioner (liquid CYA) instead of Dichlor to build up the CYA -- that's up to you. The liquid CYA is around twice as expensive as using Dichlor, accounting for the chlorine you would need anyway, but the liquid CYA does have the advantage of getting you to 30 ppm CYA right away.

[NewB@Spa]

Maybe I will try the liquid conditioner the next fill in the spring. I am always up for a new and hopefully improved process

[ThomasSE]

Yeah don't you love how the manufacturers and pool stores all send you in a death spiral trying to get the balance right. I just did a fill and my TA is ~ 80 and my Ph is about 8.1

I am going to add more Ph down this afternoon and remeasure both Ph and TA. I expect TA to lower to about 60-70 which I can live with as long as my Ph stays stable. When I added the Borates (Boric acid) I only added ~8oz because I figured I could always add more later. Chem Geek do you recommend adding the remaining 8oz of Boric Acid?

I am still in the adding Dichlor stage so I can get my CYA to ~25 (measured, not calculated) then switch to bleach.

Heh. Death spiral is what it feels like.

Anyway, yesterday I added more ph-down, I wanted to lower it from 8.0 to 7.5. Looked at the ph-down "manual" and it said one tablespoon per 400 liters/105 gallons to lower it 0.2. So I added 7 tablespoons of it, my tub hold 1438 litres/380 gallons. Wooooh, ph got down to 6.2...not good. TA was also very low. Added 125 grams/0.27 lbs of "baking soda" and waited an hour.

Now PH is 7.5 and TA is 80 so I'm "happy".

So I should be ok for now?

I'm thinking that for the next refill I will balance TA to 160-170 which is a bit high, wait for 24 hrs then use PH-down. Good or bad?

I don't know if they sell "Borates" overhere but I will look for it.

[quantumchromodynamics]

Heh. Death spiral is what it feels like.

Anyway, yesterday I added more ph-down, I wanted to lower it from 8.0 to 7.5. Looked at the ph-down "manual" and it said one tablespoon per 400 liters/105 gallons to lower it 0.2. So I added 7 tablespoons of it, my tub hold 1438 litres/380 gallons. Wooooh, ph got down to 6.2...not good. TA was also very low.

You should use thepoolcalculator to determine the correct amount of chemicals to add. It shows that to lower the pH from 8.0 to 7.5 you would use 0.5 to 0.8 ounces (volume) of dry acid (different results at the pH section vs. "Effects of adding Chemicals" section).

[Edit] The "Effects of adding chemicals" section uses ounces of weight. The "Effects of adding chemicals" section gives a 0.5 pH decrease when adding 1.13 ounce weight of dry acid, which converts to 0.815 ounces volume.

I'm not sure why the pH section gives a different reading than the "Effects of adding chemicals" section. Although, the calculator does specify that pH change will be approximate. The two sections must use different calculations to determine pH change.[End edit]

You can use Google or wolframalpha to convert ounces into tablespoons. 0.5 ounces = 1 TBS (tablespoon), 0.8 ounces (volume) = 1.6 tablespoon.

Just put the question in the search box:

0.8 ounces in tablespoons

and it will give the answer.

Are you sure that the reference you checked for the amount didn't specify "teaspoons" instead of "tablespoons"?

1 US tablespoon = 3 US teaspoons. 7/3 = 2.33 tablespoons, which makes more sense.

I'm thinking that for the next refill I will balance TA to 160-170 which is a bit high, wait for 24 hrs then use PH-down. Good or bad?

160 ppm is way too high. You should initially balance your TA to about 80 ppm.

[ThomasSE]

My thought was that getting TA to 160 then use PH down which also lowers TA. So when I lower ph from 8.5 to 7.5 the TA should be ~100(My tapwater is ph 8.5.)

But maybe 160 is too high, let's say 140-150.

Maybe this is a bad idea?

Also, spoke with the dealer here today, they're saying that TA is more important than PH...feels wrong when reading all the posts here

Regarding tablespoons/teaspoons I might have got it wrong, have to recheck. "Funny thing" is that the HS dealer in Scandinavia has its HQ in norway...so all the text on the chems are in norwegian...and I'm swedish. (But they are pretty similar tough)

And then I'm trying to translate everything to english when I post here... Life is hard sometimes

[quantumchromodynamics]

Strange is that the manufacturer of the SPA wants me to have 100-150 TA and 7.4-7.6 ph. Seems impossible with the chems I got with the tub.

The buffering effect of carbonate alkalinity works in two ways to buffer pH drop. One is when an introduced acid causes bicarbonate to become (carbonic acid/solvated carbon dioxide), and the second is when the solvated carbon dioxide off-gasses.

Most manufacturers do not understand that the level of carbonate alkalinity directly affects the rate of carbon dioxide loss and the effect of that loss on the pH.

HCO₃^- + H⁺ --> (CO₂)(H₂O) --> H₂O + CO₂ (g)

High water temperatures and lots of aeration cause carbon dioxide to be lost at an increased rate. Loss of carbon dioxide causes pH to increase.

pH and TA are both important. TA has two purposes; one is to provide the carbonate portion of the CSI (Calcite Saturation Index. Calcite is calcium carbonate). The other purpose of TA is to provide a buffer for the pH.

If your TA is over about 80, then your pH is going to continue to rise due to the amount of excess carbon dioxide.

You can use http://translate.google.com/?hl=en# to translate. It works fairly well.

You should use thepoolcalculator to determine your CSI. You should keep your CSI between -0.3 and 0.0.

[NewB@Spa]

Heh. Death spiral is what it feels like.

Anyway, yesterday I added more ph-down, I wanted to lower it from 8.0 to 7.5. Looked at the ph-down "manual" and it said one tablespoon per 400 liters/105 gallons to lower it 0.2. So I added 7 tablespoons of it, my tub hold 1438 litres/380 gallons. Wooooh, ph got down to 6.2...not good. TA was also very low.

You should use thepoolcalculator to determine the correct amount of chemicals to add. It shows that to lower the pH from 8.0 to 7.5 you would use 0.5 to 0.8 ounces (volume) of dry acid (different results at the pH section vs. "Effects of adding Chemicals" section).

You can use Google or wolframalpha to convert ounces into tablespoons. 0.5 ounces = 1 TBS (tablespoon), 0.8 ounces (volume) = 1.6 tablespoon.

Just put the question in the search box:

0.8 ounces in tablespoons

and it will give the answer.

Are you sure that the reference you checked for the amount didn't specify "teaspoons" instead of "tablespoons"?

1 US tablespoon = 3 US teaspoons. 7/3 = 2.33 tablespoons, which makes more sense.

I'm thinking that for the next refill I will balance TA to 160-170 which is a bit high, wait for 24 hrs then use PH-down. Good or bad?

160 ppm is way too high. You should initially balance your TA to about 80 ppm.

I agree with quantum, tablespoons is almost never a measure you want to add any chemicals with, especially in a spa. Teaspoons is almost always prescribed. You can always add more - the death spiral starts when you add too much...I am glad your Ph is good, but again I agree with quantum that a TA of 160 is too high. By using Nitro's approach by the time you are completed the Dichlor adds (before the bleach) your TA may drift down from ~80 to ~60 (which should be fine). Using your spa volume (ignoring all other readings) the Pool Calculator http://www.poolcalculator.com/

recommends adding .7oz by weight using a conversion calculator - http://www.gourmetsleuth.com/cooking-conve...onversions.aspx the .7oz (~19 grams) converts to 1.3 tablespoons. So you can see why 7 tablespoons drove your Ph so low.

[quantumchromodynamics]

Using your spa volume (ignoring all other readings) the Pool Calculator http://www.poolcalculator.com/

recommends adding .7oz by weight using a conversion calculator - http://www.gourmetsleuth.com/cooking-conve...onversions.aspx the .7oz (~19 grams) converts to 1.3 tablespoons. So you can see why 7 tablespoons drove your Ph so low.

The pool calculator shows 0.702 ounce by weight or 0.468 ounce by volume. (You can get extra accuracy by adding a few zeros onto the spa volume). When converting to tablespoons, you have to use the volume measurement.

The density of dry acid (sodium bisulfate) is about 1.387 to 1.5 ounce weight per ounce of volume (It looks like the poolcalculator uses 1.5 ounce weight per ounce of volume).

NaHSO₄

http://www.thepoolteammd.com/pdfs/SpaGuard...20Decreaser.pdf

DENSITY: 83 lb/cu ft (bulk)

[quantumchromodynamics]

The amount of solvated carbon dioxide is also highly dependent on the pH. Here are some values of the percent of carbonic acid/solvated carbon dioxide on a molar basis with the bicarbonate ion.

pH..........% Solvated Carbon Dioxide

7.0..........18.3

7.1..........15.1

7.2..........12.4

7.3..........10.1

7.4............8.2

7.5............6.6

7.6............5.3

7.7............4.3

7.8............3.4

7.9............2.7

8.0............2.2

As you can see, there is 1.94 times as much carbon dioxide in the water at a pH of 7.5 as there is at a pH of 7.8. This is why there is less pH rise when you use a higher pH even though it might seem counter-intuitive. (pKa for carbonic acid/solvated carbon dioxide = 6.35).

The pKa for carbonic acid is about 3.45 to 3.58. However, only about 0.15 to 0.2 % is carbonic acid while about 99.8 to 99.85 % is solvated carbon dioxide. This makes the effective pKa about 6.35.

The formula is 10^X/ (1 + 10^X) = Percent of the acid base pair that is acid. X = pKa - pH.

[chem geek]

This chart shows something similar to what QCD showed above, but lists the factor of how much more carbon dioxide there is in the water than the equilibrium amount that would occur due to the carbon dioxide in the air. You can see that lower pH or higher TA puts things more out of equilibrium. Because it seems that the rate of outgassing of carbon dioxide varies with the square of the TA (this effect not being shown in the table which just shows concentration ratios, not outgassing rates), a higher TA results in a faster pH rise in spite of its greater pH buffering.

As for The Pool Calculator, the top part of the table that calculates how much chemical to add has an approximate estimate based on the TA and Borates level while the calculation in the "effects of adding chemicals" section assumes a fixed TA closer to 80 ppm with smalller pH changes (as described in the "Note:" in that section).

The effect of acid on TA is an exact relationship. The only estimated effect in The Pool Calculator is that for pH. My spreadsheet has a precise calculation, but it is not easily translated to simpler formulas so The Pool Calculator uses an estimated formula and table approach. Also, as one gets the pH closer to 7.0, things become very non-linear so mis-estimating the pH by even 0.1 leads to large changes in the amount of acid needed which is partly why one should add less than calculated and then remeasure.

[flyguyscott]

I had the same issue, with a TA of 80-100 my pH would go through the roof, I was constantly battling to get the pH down while keeping the TA where "it's supposed to be".

now, I have a TA of 40 and a pH of 7.8 and all is perfect. With a TA that low, it won't let my pH rise much higher.

For the last couple of week now I haven't had to add any chemicals other than shock (as I have a salt system).

Good luck, hope this helps.

[quantumchromodynamics]

A value of 1.0 means there is twice as much Carbon Dioxide in the water compared to the equilibrium amount.

A value of 2.0 means there is three times as much Carbon Dioxide in the water compared to the equilibrium amount and outgasses twice as fast as 1.0 - Richard's chart

Richard, I'm not sure I understand how your numbering system works. What would the other values mean? 3-100?

Also, that chart is for 80 F, do you have the same chart for hot tub temperatures?

[chem geek]

A value of 1.0 means there is twice as much Carbon Dioxide in the water compared to the equilibrium amount.

A value of 2.0 means there is three times as much Carbon Dioxide in the water compared to the equilibrium amount and outgasses twice as fast as 1.0 - Richard's chart

Richard, I'm not sure I understand how your numbering system works. What would the other values mean? 3-100?

Also, that chart is for 80 F, do you have the same chart for hot tub temperatures?

The chart shows "[actual aqueous CO2] / [equilibrium aqueous CO2] - 1". So at equilibrium, it's 0. "1" means twice as much CO2 in the water as there would be at equilibrium with air. Using this scale, a 10 has twice as much "excess CO2" as a 5. If the outgassing rate were linearly related to the concentrations, then this would be a decent scale where 10 would outgas twice as fast as 5. The "- 1" removes the reverse rate component of CO2 going into the water and therefore is the net rate (outgassing minus ingassing). So "10" has 11 times the amount of CO2 in the water as would be there at equilibrium.

Wojtowicz did some experiments that found that the outgassing rates weren't linearly based on the TA (or carbon dioxide concentration at a given pH), but rather varied with the square of TA (or such concentration). I need to remove the "outgasses twice as fast as 1.0" that I wrote in that table before I read about the Wojtowicz experiments.

I don't have a chart for spa temps (104F) but the outgassing rate would be much faster at all out-of-equilibrium conditions as higher temperatures have all chemical reactions and physical (molecular inter-phase) processes go faster.

[quantumchromodynamics]

OK, thanks for explaining. This definitely helps explain why pH rise happens so fast when the carbonate alkalinity is too high and/or the pH is kept too low.

[PaulR]

[Edit] The "Effects of adding chemicals" section uses ounces of weight. The "Effects of adding chemicals" section gives a 0.5 pH decrease when adding 1.13 ounce weight of dry acid, which converts to 0.815 ounces volume.

I'm not sure why the pH section gives a different reading than the "Effects of adding chemicals" section. Although, the calculator does specify that pH change will be approximate. The two sections must use different calculations to determine pH change.[End edit]

The pH section takes TA and borates into consideration. The "Effects of adding chemicals" section assumes nominal values for the calculations. In either case the answer is approximate.

--paulr

[NewB@Spa]

Right now I am having a bear of a time getting my Ph stable. Performed a Spa purge, drain and refill about 2 weeks ago and still working to stabilize the readings. I have a 425 gal Spa which I keep at approximately 102. I have just switched over to bleach after reaching ~30 CYA. My CH=~150, Borates ~50. and my TA~100. That is the hard part. When I initially balanced I had a TA of 80 and Ph of ~7.6. Now in a little over a week Ph has shot up to 8. I added Ph down to get it to 7.5 and for a day it work, but my TA went down to 50. Added baking soda to get it to 80, now it is 100

What am I doing wrong?

[quantumchromodynamics]

My CH=~150, Borates ~50. and my TA~100. That is the hard part. When I initially balanced I had a TA of 80 and Ph of ~7.6. Now in a little over a week Ph has shot up to 8. I added Ph down to get it to 7.5 and for a day it work, but my TA went down to 50. Added baking soda to get it to 80, now it is 100

What am I doing wrong?

You should have left your TA at 50-60. You need to balance your TA based on the pH. If your pH is constantly too low, then your TA is too low. If your pH is constantly too high, then your TA is too high. If your pH is constantly good, then your TA is good

Using a TA of 70-80 will work OK while using dichlor. Once you switch over to bleach, you have to use a lower TA. Most people find 50-70 to work well.

[NewB@Spa]

My CH=~150, Borates ~50. and my TA~100. That is the hard part. When I initially balanced I had a TA of 80 and Ph of ~7.6. Now in a little over a week Ph has shot up to 8. I added Ph down to get it to 7.5 and for a day it work, but my TA went down to 50. Added baking soda to get it to 80, now it is 100

What am I doing wrong?

You should have left your TA at 50-60. You need to balance your TA based on the pH. If your pH is constantly too low, then your TA is too low. If your pH is constantly too high, then your TA is too high. If your pH is constantly good, then your TA is good

Using a TA of 70-80 will work OK while using dichlor. Once you switch over to bleach, you have to use a lower TA. Most people find 50-70 to work well.

So should drive my Ph down (to lower TA) and then aerate to raise Ph? Not sure exactly how that works though.

[quantumchromodynamics]

Once you get your TA right, your pH will stay at the right level.