Muriatic acid lowers TA, or does it?

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duraleigh

duraleigh

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Apr 1, 2007
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Split off of First Numbers are in!. JasonLion

I think my first plan of attack will be lowering the TA a bit with MA.
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Well, here I go up on my soapbox, again. jjdurant, this has nothing to do with your quote but rather something I have seen brewing on this forum for a while.

If we stay true to the simple reasoning of BBB, we remember that muriatic does not lower TA......aeration/muriatic process does.

1. muriatic is to lower pH

2. Aeration/muriatic is the process to lower TA.

Back in the day, we simply stated muriatic lowers your pH and aeration lowers your TA. That's not technically correct but the technically correct answer is another case of us getting the forum more complex than it needs to be.

Over the last few weeks I have seen at least 3 instances of threads wherein these things have been confused and lead to misinformation.

You cannot permanently lower TA unless you aerate.

Again, I realize I'm not precise on the wording but I have sure made it less confusing (which was Ben's whole purpose).

Okay, I'm down off my soapbox.
 
Re: First Numbers are in!

Well maybe I'm wrong, and I'm here adding to the 'off-but-related-topic' of lowering TA...but it's my understanding that MA lowers BOTH, and Aeration brings the PH back to the appropriate range of 7.4-7.6 and it's repeating this process of MA/Aeration that ultimately puts the TA lower and the PH right where it needs to be?

But I agree with you, sometimes the translation gets lost or oversimplified for BBB beginners.
 
Re: First Numbers are in!

FPM,

That's a perfect example of my point of how confusing we have made it...........MA temporarily lowers both. Any permanent reduction in TA has to involve the use of aeration. If MA alone would keep TA down, we would never have to aerate.

So rather than be absolutely precise on the process, why don't we say it in such a way that everyone can understand and remember?
 
If you say that aeration lowers TA you are likely to create the wrong impression. We have actually had people set up massive amount of aeration, no acid anywhere in sight, and then ask us why their TA hasn't gone down. That isn't exactly common, but it does show that the details of the wording matter.

The more common mistake is to lower PH and TA with muriatic acid and then raise PH back up with borax and then wonder why the TA went back up. Some of the pool stores actually encourage people to lower the PH way way down in order to lower their TA, without telling them anything about why or how or even hinting at aeration in any way. Apparently the pool store simply assumes that some aeration will happen, and rather quickly at that, if the PH is simply low enough. On the next visit their PH is too low and the pool store has them raise it up again with soda ash. The net result is that the TA actually goes up, not to mention the possible damage from PH levels in the low 6s.

The next option would be to try and link the words: acid&aeration or aeration&acid. Ignoring the stylistic choices about & or "and" or - or whatever, most people won't type that. Thus, jjdurant shortens it to acid and leaves off the aeration, when he does in fact know how it works.

What we really need is some magical product that lowers the PH and causes the pool to totally foam up for just a few hours and then go back to normal, which doesn't cost much more than muriatic acid.

More seriously, I don't see any good really short and simple way to explain this. I refer people to the Pool School article, which covers the whole subject rather well in about one screen of text and refers people who are interested to waterbear's substantially more detailed version.

The shortest possible way I can come up with saying it is
Add acid to lower the PH and TA, and then aerate to raise the PH back to where it was while leaving the TA lower.
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Or the rather more abstract
A combination of acid and aeration is used to lower TA.
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which is still correct, but doesn't actually tell you how to do it.
 
Interesting.. I have to say though.. MA seemed to do the trick last year.. I did some aeration with an air compressor.. but not much.

With that said.. my TA is back up to 200 from approx 150 when I closed the pool last fall. Also, my pool stays busy with kids all summer. So I am getting plenty or aeriation there. Nonetheless.. Was able to drop my TA over 120 by using MA and kids splashin. I wish I knew which method was more effective by itself. :)

I plan to skip the MA for now and aerate like crazy.. will see what happens! I will be in touch!
 
jjdurrant said:
I plan to skip the MA for now and aerate like crazy.. will see what happens! I will be in touch!
Click to expand...

And
duraleigh said:
FPM,

That's a perfect example of my point of how confusing we have made it...........MA temporarily lowers both. Any permanent reduction in TA has to involve the use of aeration. If MA alone would keep TA down, we would never have to aerate.

So rather than be absolutely precise on the process, why don't we say it in such a way that everyone can understand and remember?
Click to expand...

I guess I'm still confused. If he skips the MA for now, aeration won't do a thing for the TA, it will only raise the PH, right?
 
MA lowers both PH and TA. Aeration raises PH and leaves TA alone. When used together in the right combination, PH stays the same and TA goes down.

You can actually skip the aeration, if you are not in a hurry. There will always be some natural aeration.

You can not skip the acid. [[The only half an exception to this is that you can use a product that don't say acid on the label, like trichlor, but which will still lower the PH and TA because it is acidic.]]
 
MA lowers both PH and TA.
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Not permanently, if I remember Ben's explanation (PF is down again, I think).

I do remember that he was virtually the first one to ever offer this method as a way to permanently lower TA and his emphasis was on permanent. I have thought about it (in my red-neck laymen's terms) as aeration changing the "ratio" of TA to pH. That they slide up and down together unless you aerate and then TA doesn't come back up with pH. I know that's scientifically absurd but it made it easy for me to understand it.

I hope this thread continues a while......it's becoming even more apparent to me just how few of us truly have a good grasp of the process. :lol:
 

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duraleigh said:
Not permanently, if I remember Ben's explanation (PF is down again, I think).
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I don't believe that's true. Strong acid lowers both the pH and the TA. In fact, 25-1/2 fluid ounces of Muriatic Acid (31.45% Hydrochloric Acid) will lower the TA in 10,000 gallons by 10 ppm and this is independent of starting pH or TA.

This lowering is permanent IF nothing else happens -- that is, if there is no aeration/outgassing or addition of other chemicals including evaporation and refill, etc. It's not that the aeration makes the change permanent, but rather that when you add strong acid to lower both pH and TA, you now have a pH that is (usually) too low. If you then try and raise it through any means other than aeration (i.e. through chemical addition of some sort of base), then both the pH and TA will rise back up. This is the classic see-saw effect. If one uses pH Up to raise the pH, you actually end up with an even higher TA than when you started because pH Up adds to carbonates -- it's not just a base.

The procedure Ben came up with is based on two key steps and principles. One is that the way to raise the pH with no change in TA is to aerate the water. The other is that the process goes faster (i.e. aeration is more effective because outgassing is faster) at lower pH.

Aeration isn't a requirement to make things permanent, nor is doing the process at a lower pH. These factors just make the process go faster. As Jason points out, you can simply add acid whenever the pH rises and slowly over time the TA will drop. Of course, this assumes that there isn't anything happening to have the TA increase. In many pools, evaporation and refill increases TA because fill water usually has a decent amount of TA so this gets added to the pool.

It's also a mistake to think that doing the procedure to lower the TA uses less acid than just adding a smaller amount of acid over time whenever the pH rises. The amount that the TA drops is based on the amount of acid that is added. It doesn't matter whether it's added quickly or over time. The TA lowering procedure simply accelerates a process that would occur more slowly anyway. You do the procedure because you have a problem -- the high TA is causing the pH to rise frequently and you want to reduce its rate of rise OR your high TA leads to a scaling condition so you want to avoid that.

Look at this chart which shows how far out-of-equilibrium pool water is with respect to the air. That is, the number is proportional to how much more carbon dioxide there is in the pool than there should be if in equilibrium with the air. Notice how the numbers are much higher at lower pH and at higher TA. Higher numbers mean faster outgassing, though outgassing rates are more complicated than shown (they seem to be proportional to the square of the TA, whereas the table doesn't show that).

Richard
 
This lowering is permanent IF nothing else happens -- that is, if there is no aeration/outgassing or addition of other chemicals including evaporation and refill, etc.
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Hey, Richard,
I seem to remember outgassing occurs naturally in most pools and that aeration only accelerates it. I must have that mixed up because that would seem to indicate that TA will naturally drop over time.

My pool, a non-swg, has a natural pH rise that requires acid 2-3 times seasonally. I have not kept records, but I seem to clearly remember that the TA rises right along with the pH....am I "disremembering", again? :lol:
 
PaulR said:
So, does "dry acid" lower TA the same way muriatic does? I've been poking at my spa with dry acid the past day or so, and the TA seems to be kind of reluctant to drop.
--paulr
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Yes, it should, but remember that the pH moves more than the TA. For example, adding acid to go from a pH of 7.8 to 7.5 when the TA is around 80 ppm would have the TA drop to 77 which would still measure as 80. It would take several acid additions of this sort before you might notice a drop of 10 ppm in TA.
 
duraleigh said:
Hey, Richard,
I seem to remember outgassing occurs naturally in most pools and that aeration only accelerates it. I must have that mixed up because that would seem to indicate that TA will naturally drop over time.

My pool, a non-swg, has a natural pH rise that requires acid 2-3 times seasonally. I have not kept records, but I seem to clearly remember that the TA rises right along with the pH....am I "disremembering", again? :lol:
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TA will only drop over time if there is some sort of acid addition. If there is no acid addition, then the pH will rise over time (from the outgassing), though as the pH rises its rate slows down.

I suspect that your situation is similar to my own where I too add acid every month or two yet I see a small TA rise over the course of the summer season. Most likely it's the evaporation and refill, though with my pool cover there shouldn't be a lot of that. Or there could be some other mysterious source I'm not aware of.
 
duraleigh said:
that would seem to indicate that TA will naturally drop over time.
Click to expand...

Yes it does. Or in my case TA stays stable. I have a TA over 200 ppm in my fill water and we have rain only in the winter. So during the summer, TA is being added by the boat loads to replace evaporated water. Not because I want to but because I have no choice. So by adding MA continuously, I can keep the TA below 100 ppm and usually below 90. Of course it keeps the PH in check at same time but if MA did not lower TA, my TA would be pretty high. I do not nor will I ever bother to aerate. Not necessary in my mind, it would only speed up the process but I'm not in a hurry. The constant acid feed takes care of both PH and TA at the same time and the best part is it is very stable.

Again, this gets back to your other post. I firmly believe that you can find an equilibrium in almost any pool to minimize the amount of chems added and the maintenance required. However, it may not fall to within normal ranges and may require some out of the box thinking.
 
The whole concept is a bit counter intuitive....adding acid (it can be muriatic, dry acid, or sulfuric--the end result will be the same) will lower both pH and TA. However, we really don't want to drop the pH that low because it can cause problems. This is why we say to only drop it to 6.8 to 7.0. This is not really going to drop the TA by that much. It really depends on where we are starting with the TA. Now if we do nothing the pH will rise because of outgassing. However, since we need to repeat this process to get the TA down to where we want it we need to speed up the outgassing so we aerate. All this does is speed up the pH rise. We then repeat the process of dropping the pH (and the TA), testing our TA to see if it's low enough, then either waiting for the ph to rise on it's own or aerating to make the outgassing faster until the TA is where we want it when we test.

When we add acid we convert some of the bicarbonate in the water (which is the measurable part of TA) to carbon dioxide dissolved in water or carbonic acid. This is what club soda is also. If we make the 'club soda' we have just created in our pool go flat (outgas) by shaking the bottle (aerating the pool) we will find that the pH has risen.

If we try and raise the pH by chemical means, whether it's soda ash, borax, or sodium hydroxide (lye) then we convert some of the carbon dioxide back into bicarbonate ions and our TA rises again. The only way to get our pH to rise without converting the carbon dioxide back to bicarbonate is by getting rid of some the carbon dioxide by causing it to gas out of the water.
Aeration just speeds this step up but it will happen anyway if everything else is left alone.

Often what I do with my customers when I test their water and need to lower their TA is I do an acid demand to see how much acid will lower the pH to 6.8 and have them put in that amount. I then tell them to come back in a week because we are not done (I also calculate the total amount of acid needed to lower their TA so they can see that!). Usually in a week their pH has risen enough to do another acid demand test and lower the pH back down. If they do have any aeration such as spillover spas or fountains I do tell them to turn them on. Sometimes it can take several weeks to lower the TA this way but it does get the job done when I know the customer will not keep on top of it and just wants to dump in some acid and come back in a week. Once we get the pH in line we usually find that the pH becomes much more stable and the frequency of acid additions goes down.

Hope this helps.
 
I had to go back and read and then re-read this thread before it clicked. I believe that I had already understood it that way but now it's clear for sure. Thanks Dave.
 

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