Pool Chemistry TA

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GlenInIdaho
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My Pool: 15X30 foot pool 15,000 gal. gunitie in ground,
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Pool Chemistry TA

Postby GlenInIdaho » Mon 22 Jun, 2009 22:58

I need some help with the pool chemistry. I have been trying to lower the TA which was at 230 to within the 80 to 120 limits. The ph was at 7.6 I added 3 gallons of muratic acid which brought the TA to 110. The ph dropped off the scale and I estimate it to be around 6.2. I have been adding soda ash to raise the ph over the last 10 days or so. I have used 8 lbs. The ph is now at 6.6 and the TA has raised to 180. I was told by the pool guy the soda ash would not raise the TA, but it is. Where to I go from here to lower the TA and raise the ph. Thanks for the help.

The pool is a 15,000 gal gunite inground pool with a sand filter.


Denali
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Pool Chemistry TA

Postby Denali » Mon 22 Jun, 2009 23:30

GlenInIdaho wrote:I need some help with the pool chemistry. I have been trying to lower the TA which was at 230 to within the 80 to 120 limits. The ph was at 7.6 I added 3 gallons of muratic acid which brought the TA to 110. The ph dropped off the scale and I estimate it to be around 6.2. I have been adding soda ash to raise the ph over the last 10 days or so. I have used 8 lbs. The ph is now at 6.6 and the TA has raised to 180. I was told by the pool guy the soda ash would not raise the TA, but it is. Where to I go from here to lower the TA and raise the ph. Thanks for the help.

The pool is a 15,000 gal gunite inground pool with a sand filter.


Hi,

First off you want to get your pH back to 7.0 or above right away. Low pH like that can damage equipment.

You won't be able to drop the TA to the level you want all at once. As you've seen the pH will drop too much. BTW, soda ash raises both pH and TA.

You need to figure out a way to aerate the water. If you have a water feature of some kind or an attached spa you can use those. Aerating the water raises pH and doesn't effect TA. So the process is, add acid to lower both pH and TA but only enough to lower the pH to about 7.0. Your TA will come down some. Use aeration to raise pH up enough where you can add acid again.

This process can take some time but it works.
RMS1
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Pool Chemistry TA

Postby RMS1 » Mon 17 Aug, 2009 22:56

GlenInIdaho wrote:I need some help with the pool chemistry. I have been trying to lower the TA which was at 230 to within the 80 to 120 limits. The ph was at 7.6 I added 3 gallons of muratic acid which brought the TA to 110. The ph dropped off the scale and I estimate it to be around 6.2. I have been adding soda ash to raise the ph over the last 10 days or so. I have used 8 lbs. The ph is now at 6.6 and the TA has raised to 180. I was told by the pool guy the soda ash would not raise the TA, but it is. Where to I go from here to lower the TA and raise the ph. Thanks for the help.

The pool is a 15,000 gal gunite inground pool with a sand filter.


This is very easy to fix, if you do it right. Central Oregon tap water is 8.2 pH and 30 Alk. I can get the numbers to where they should be within a matter of hours. Pool Operator of YMCA.

Sodium bicarb works for both pH and alk. Pump on and water moving, broadcast the bicarb around the perimeter of the pool, starting in the deep end and work around. Do this at night and retest in the morning. Get your reading around 7.6-7.8, not 7.2.

Next is the alk. The next night turn pump off and water motionless. Add 1/4 bottle of of acid in deep end. In the morning turn pump back on and allow to circulate, 2-3 hours, then recheck alk. add more acid if needed. To raise alk. use bicarb with method same as to lower it.

http://www.clean-pool-and-spa.com/swimming-pool-ph.html
http://www.clean-pool-and-spa.com/pool-alkalinity.html
chem geek
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Pool Chemistry TA

Postby chem geek » Tue 18 Aug, 2009 00:06

You've got to be kidding me! Use sodium bicarb for both raising pH with one technique and raising TA with another? Yes, different amounts of rates of addition and circulation will cause different amounts of outgassing so with aeration you'll get more of a pH rise while without you'll get more of a TA rise, but generally you'll always get the TA rise so if the TA is already high you shouldn't be adding baking soda, period. You are simply mixing two techniques together -- adding baking soda and aeration.

To raise the pH without changing the TA, just aerate the water. If the TA is already high, then the pH will rise more quickly anyway.

If the pH and TA are both to be raised, especially if the pH is quite low, then using sodium carbonate (pH Up) will raise the pH a lot more than the TA though both will be raised. To raise the pH with half the rise in TA, use 20 Mule Team Borax. And as I wrote above, to raise the pH with no change in TA, aerate the water.
RMS1
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Pool Chemistry TA

Postby RMS1 » Fri 21 Aug, 2009 20:14

GlenInIdaho wrote:I need some help with the pool chemistry. I have been trying to lower the TA which was at 230 to within the 80 to 120 limits. The ph was at 7.6 I added 3 gallons of muratic acid which brought the TA to 110. The ph dropped off the scale and I estimate it to be around 6.2. I have been adding soda ash to raise the ph over the last 10 days or so. I have used 8 lbs. The ph is now at 6.6 and the TA has raised to 180. I was told by the pool guy the soda ash would not raise the TA, but it is. Where to I go from here to lower the TA and raise the ph. Thanks for the help.

The pool is a 15,000 gal gunite inground pool with a sand filter.


Chem Geek, if you read the post it says his TA was a high level of 230 and the pH was 7.6, within range. He added acid which brought the TA down to 110, within range, but now his pH is way down, 6.2. Then he added soda ash to bring up the pH, now at 6.6, which had raised, but so to his TA, now 180. His question is how to lower the alkalinity and raise the pH. I outlined the proper technique in my post, which is correct. I have an 80,000 gallon YMCA pool with 2000-3000 swimmers per week that I take care of.

I use these techniques and "No, I'm not kidding you!!" they do work.

Our fill water is pH of 8.2 and Alkalinity of 30, two extremes, and I can balance the water with one application of chemicals at night and it can be ready to swim in by 5am the next morning when the Y opens.

People want simple answers to basic questions and I give it to them.
RMS1
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Pool Chemistry TA

Postby RMS1 » Fri 21 Aug, 2009 20:16

GlenInIdaho wrote:I need some help with the pool chemistry. I have been trying to lower the TA which was at 230 to within the 80 to 120 limits. The ph was at 7.6 I added 3 gallons of muratic acid which brought the TA to 110. The ph dropped off the scale and I estimate it to be around 6.2. I have been adding soda ash to raise the ph over the last 10 days or so. I have used 8 lbs. The ph is now at 6.6 and the TA has raised to 180. I was told by the pool guy the soda ash would not raise the TA, but it is. Where to I go from here to lower the TA and raise the ph. Thanks for the help.

The pool is a 15,000 gal gunite inground pool with a sand filter.


Chem Geek, if you read the post it says his TA was a high level of 230 and the pH was 7.6, within range. He added acid which brought the TA down to 110, within range, but now his pH is way down, 6.2. Then he added soda ash to bring up the pH, now at 6.6, which had raised, but so to his TA, now 180. His question is how to lower the alkalinity and raise the pH. I outlined the proper technique in my post, which is correct. I have an 80,000 gallon YMCA pool with 2000-3000 swimmers per week that I take care of.

I use these techniques and "No, I'm not kidding you!!" they do work.

Our fill water is pH of 8.2 and Alkalinity of 30, two extremes, and I can balance the water with one application of chemicals at night and it can be ready to swim in by 5am the next morning when the Y opens.

People want simple answers to basic questions and I give it to them.
rvpwt
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Pool Chemistry TA

Postby rvpwt » Sat 22 Aug, 2009 08:57

My test kit is showing that my TA is 60 but my ph is 8.2. Is this possible. I know that if the TA is off it is not possible to balance the ph and keep everything in harmony.. What is my next step?
chem geek
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Pool Chemistry TA

Postby chem geek » Sat 22 Aug, 2009 12:12

RMS1,

With your low TA of fill water of 30 ppm, of course baking soda helps raise it since that is primarily what it does. 22.4 ounces weight of baking soda (Alkalinity Up; sodium bicarbonate) in 10,000 gallons will raise the Total Alkalinity (TA) by 10 ppm no matter how you add it. The only difference via method of addition is whether you promote outgassing which by itself will raise the pH with no change in TA (so in combination you increase pH and TA) and you could do the outgassing separately if you wanted to (running pumps on high and pointing returns upwards; running waterfalls and fountains; splashing). So adding baking soda is going to increase the TA regardless -- it is not a good way to increase pH without increasing TA. You could use it to raise both but if the pH is very low then using pH Up (sodium carbonate) would be more efficient.

14.1 ounces weight of soda ash (pH Up; Arm & Hammer Super Washing Soda; sodium carbonate) in 10,000 gallons will raise the TA by 10 ppm no matter how you add it. However, in this case, the pH is raised substantially, but how much it is raised depends on the initial pH and TA and how much outgassing is induced. With no outgassing, starting with a pH of 7.5 and TA of 100 the 14.1 ounces of soda ash in 10,000 gallons would raise the pH to 7.9.

With your pool, the pH in the fill water is high so you would add baking soda to raise the TA and acid to lower both TA and pH so you'd have to overshoot with the baking soda addition a little bit. Starting with a pH of 8.2 and TA of 30 ppm, to get to a pH of 7.5 and TA of 100 ppm it would take 171.6 ounces weight of baking soda and 16.7 ounces of full-strength Muriatic Acid (31.45% Hydrochloric Acid) in 10,000 gallons if there were no outgassing (with outgassing you would need more acid and a technically a touch more baking soda though it would be well within measuring limits of TA). Of course, this assumes the entire pool started out with fill water; for normal evaporation or splash-out and refill the amount of needed adjustment will be much smaller. Mostly in an active pool, the pH will rise if using hypochlorite sources of chlorine due to the carbon dioxide outgassing and ironically having a lower pH results in more pH stability and less acid that needs to be added to keep the pH down.

The "acid column" or "slug" method for lowering TA was debunked here . It's not that different methods of addition can't have some influence on outgassing, but that intentional aeration is a much more efficient method of increasing the pH with no change in TA and the acid column method is dangerous due to the very low pH staying in one place near pool surfaces.

In the case of GlenInIdaho, starting with a pH of 7.6 and TA of 230 in 15,000 gallons, then adding 3 gallons of Muriatic Acid would lower the pH to 6.22 and the TA to 130 ignoring any outgassing (he measured the pH being around 6.2 just as predicted and the TA being 110 which is close and within measurement error for two measurements). He then added 8 pounds of soda ash which would have raised the pH to 6.5 and the TA to 190 ppm (Glen got pH 6.6 and TA of 180, again within measurement error). Since his TA did not need to be raised after adding acid, he wanted to raise the pH with no change in TA and the way to do that is with aeration of the water since outgassing of carbon dioxide raises the pH with no change in TA. If he were to add any sort of base to raise the pH, then the TA would have risen as well -- pH and TA move together in lock-sync when adding acids and bases to the water. This is why trying to lower TA should NEVER be done only through a combination of adding acids and bases and instead should be done following the procedure outlined in this post. It requires outgassing which is accelerated by aeration and low pH. In fact, if one adds soda ash as the base, one increases TA even more making the problem worse. Soda Ash is chemically identical to a combination of caustic soda (lye; sodium hydroxide) which is a pure base and baking soda (Alkalinity Up; sodium bicarbonate).

So you're trying to get his pH up via baking soda would have increased the TA as well -- even more so than his using pH Up or even 20 Mule Team Borax. His situation with high TA, or a TA he didn't need to increase, is not like yours with low TA fill water. Notice how I was able to calculate and predict his numbers almost exactly (using my spreadsheet here , but it is not for novice users). The only variable would be outgassing and it appears his pool didn't have much.

Richard
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Pool Chemistry TA

Postby chem geek » Sat 22 Aug, 2009 12:25

rvpwt wrote:My test kit is showing that my TA is 60 but my ph is 8.2. Is this possible. I know that if the TA is off it is not possible to balance the ph and keep everything in harmony.. What is my next step?

Yes this is very possible. You need to understand that Total Alkalinity (TA) has TWO effects. One is to buffer pH so that would tend to make the pH more stable or resistant to change from outside influences (acids and bases). However, the other effect is that higher TA is a source of rising pH itself since it leads to faster carbon dioxide outgassing and this increases the pH of the pool over time (or if acids are being added to the pool, such as using Trichlor pucks/tabs, then this decreases the rate of pH drop over time from such acids).

So the proper TA level for your pool depends on the source of chlorine you are using since acidic sources of chlorine such as Trichlor pucks/tabs should have a higher TA level to help offset the acidity. On the other hand, if you are using hypochlorite sources of chlorine, such as chlorinating liquid, bleach, Cal-Hypo or lithium hypochlorite, then your TA can be on the low side to reduce the rate of pH rise. Usually at a TA of 60 ppm, you wouldn't have much pH rise over time using hypochlorite sources of chlorine unless you've got a lot of aeration (i.e. waterfalls, fountains, spillovers, etc.).

If you were to add 12.3 fluid ounces of full-strength Muriatic Acid (31.45% Hydrochloric Acid) for every 10,000 gallon in your pool, then you would lower the pH to 7.5 and the TA would drop to 55 ppm. If you wanted to raise the TA, you could do so by adding baking soda (Alkalinity Up; sodium bicarbonate) where as noted in the previous post 22.4 ounces weight of baking soda in 10,000 gallons raises the TA by 10 ppm. Depending on how much outgassing there is, you may notice a pH rise when you add the baking soda though if you do so by very slowly adding it over a return flow with the pump running (but returns not pointed upwards -- i.e. not increasing aeration much), then this effect should be minimized.

There are other sources of rising pH as well including new plaster (or replastering) since the curing of plaster causes the pH to rise rather quickly, especially in the first month, but continues for months slowing down after 6-12 months (though still technically happening at a slower rate). Curing adds calcium hydroxide to the water so increases the pH and also the Calcium Hardness (CH).

So as for your next step, it depends on your specific situation. For sure, you need to add acid to lower the pH, but as for what level of TA you should target it depends on your source of chlorine and whether your plaster is new (if you have a plaster pool; obviously doesn't apply to vinyl). If you are using hypochlorite sources of chlorine and find that your pH is more stable at the lower TA level, then if your pool isn't vinyl you should increase your Calcium Hardness (CH) to compensate and keep the saturation index near zero. You can use The Pool Calculator to calculate it and for dosages.

Richard
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Pool Chemistry TA

Postby nocturnalsheep » Mon 31 Aug, 2009 19:01

Just in case...one thing that should be considered is the cyanuric acid level because around 30% of the cyanuric acid reading should be subtracted to the level of alkalinity that was tested to get the adjusted total alkalinity. With a pH of 7.6, as long as it is holding, the alkalinity doesn't need to be messed with. Alkalinity should be brought to whatever level holds the pH in the specific body of water. I have taken care of pools that held their pH with alkalinity levels of as low as 50 and as high as 220. There are other factors to take into account when this is the case (such as the saturation index), but for the sake of the pH, just find the alkalinity level that holds the pH where it needs to be (7.5-7.6 ideal). The 'ideal' range of alkalinity (80-120) is a fallacy when it comes to holding pH and can't really be applied to every pool. Every pool has it's own unique personality that needs to be assimilated and treated accordingly.

anyway...check the cyanuric acid, take 30% of the reading and subtract that from the alkalinity level that was tested and that is your true alkalinity. And don't adjust the alkalinity if your pH is holding in the appropriate range.

-Danny

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