Question on TA

[jesse-99]

When it comes to LOWERING TA, we all ready on here to lower your pH to 7.2 or 7.0 and aerate back up to 7.6-7.8 and then lower pH back down to 7.2 or 7.0 again, rinse and repeat. I guess I'm wondering, what happens in the following scenario:

Bringing pH down to 7.2: Lets say it lowers TA to "x"

Does the following then ALSO hold true?

Bringing pH down to 7.0: Lowers TA even a bit more than it would if you had lowered pH to 7.2
Bringing pH down to 6.8: Lowers TA even a bit more than it would if you had lowered pH to 7.0
Bringing pH down to 6.6: Lowers TA even a bit more than it would if you had lowered pH to 6.8

Get what I'm saying? Down the AMOUNT of pH drop (under 7.2 or 7.0) also -continue- to lower TA in accordance? -or- Whether pH to 7.2 or 7.0 or 6.8 or 6.6, doesn't really matter, its only going to a lower to "x".?

(Note, obviously I know a pH of sub 7.0 isn't good and I'm not going to be lowering my pH to 6.6 intentionally, I'm just curious about the math/chemistry on the above question) --- My pool is closed already so please don't come at me with pointing fingers and glaring eyes,

 

[JoyfulNoise]

The amount by which the TA lowers is directly proportional to the amount of acid added. It’s a direct chemical reaction that PoolMath calculates exact amounts for. You use the “Effects of Adding Chemicals” to calculate that. The drop in pH is a response to multiple factors based on the buffering species in the water.

So you can always drop the TA by a prescribe amount by just adding the right among of acid and let the pH drop and recover on its own. I typically add enough acid in my pool to drop the TA by 10ppm and then let the pH do whatever it will do.

 

[flynwill]

he amount by which the TA lowers is directly proportional to the amount of acid added.

How do Borates factor into that? I note that somewhere in these pages I saw the recommendation to lower TA before adding borates because it will take more Acid to do so after. I assume that was because it generally will take more acid to lower pH an given amount due to the additional buffering from the Borates.

 

[jesse-99]

The amount by which the TA lowers is directly proportional to the amount of acid added. It’s a direct chemical reaction that PoolMath calculates exact amounts for. You use the “Effects of Adding Chemicals” to calculate that. The drop in pH is a response to multiple factors based on the buffering species in the water.

So you can always drop the TA by a prescribe amount by just adding the right among of acid and let the pH drop and recover on its own. I typically add enough acid in my pool to drop the TA by 10ppm and then let the pH do whatever it will do.

This is exactly what I was looking for. I totally forgot to check the Effects of Adding Chemicals in Pool Math, that answers that! Thx.

 

[mgtfp]

How do Borates factor into that? I note that somewhere in these pages I saw the recommendation to lower TA before adding borates because it will take more Acid to do so after. I assume that was because it generally will take more acid to lower pH an given amount due to the additional buffering from the Borates.

As Matt had said, the TA reduction is exactly proportional to the amount of acid added, with or without Borates.

But with Borates the pH-change will be smaller.

 

[Bperry]

How do Borates factor into that? I note that somewhere in these pages I saw the recommendation to lower TA before adding borates because it will take more Acid to do so after. I assume that was because it generally will take more acid to lower pH an given amount due to the additional buffering from the Borates.

Note that with the borates, the “total amount” of acid needed to lower the pH won’t change, but the frequency at which you need to add the acid to maintain a specific pH does go down slightly as borates are added. It takes more acid to affect a pH reduction when borates are present, but the borates slow down the pH rise so kind of a pick your poison situation.

 

[AUSpool]

Note that with the borates, the “total amount” of acid needed to lower the pH won’t change, but the frequency at which you need to add the acid to maintain a specific pH does go down slightly as borates are added. It takes more acid to affect a pH reduction when borates are present, but the borates slow down the pH rise so kind of a pick your poison situation.

This is correct but still a bit confusing, best to say “the total amount over a given time period”. With 50ppm borate the amount of acid required to lower the pH from 7.8 to 7.0 is greater then without borates.

In theory the rate of pH increase after lowering the pH to 7.0 would be quite similar with or without borates until the pH climbs to ~7.5-7.6. After a pH of 7.6 the % of borates starts to increase at a greater rate and the buffering effect of borates becomes greater.

 

[Gary Davis]

In taking a slightly tangential approach to the OP's question, I tend to ask myself WHY I'm doing anything to the pool chemistry.

• Why is the OP wanting to lower alkalinity

As noted in this thread already, in certain cases there are directly proportional cause-and-effect ratios (e.g., the lowering of TA is proportional to the amount of acid added), and, yet, as also noted in this thread already, some situations are NOT easily denoted to be proportional (as when the pH upper 9.1 and lower 6.1 pKa equilibria levels are approached, depending on carbonate and borate alkalinity).

One of those situations is the calcium saturation index, where the OP's signature doesn't mention the pool wall material but the avatar indicates a high chance of it being a plaster pool, which then, especially in winter, matters in terms of calcium hardness (which itself is a component of the saturation index).

I guess I'm wondering, what happens in the following scenario:
Bringing pH down to 7.2: Lets say it lowers TA to "x"
Does the following then ALSO hold true?

If the OP is asking what happens when he lowers the TA, I would suggest that an ADDITIONAL question to ask is what happens to the saturation balance as a result of lowering the TA (where lowering the TA in and of itself, would tend to need an offset of around 1:3 or 1:4 for calcium hardness).

• That is, lowering TA by 10 ppm would generally indicate a need to raise CH by three to four times that (on average) to stay balanced
• (all other things being equal)

In summary, my question is what is the OP expecting to accomplish by lowering the TA given he then has to consider what the affect is upon not only his pH (which has been adequately covered in this thread so far), but also on the effect his purposeful lowering the TA has on his resulting cold-water saturation balance (which hasn't been covered yet in this thread - and which is why I bring it up).

 

[PoolStored]

the effect his purposeful lowering the TA has on his resulting cold-water saturation balance (which hasn't been covered yet in this thread - and which is why I bring it up).

Any effect of low CSI takes months or years to develop. It is when CSI drops below -0.6 and really below -1.0 for a length of time that it should be a concern.

In a closed pool for the winter pH will rise and water temperature will fall which offset each other for the CSI.

A pool is only closed for the winter for around 5 months. Any effect on the plaster by the CSI will only be for two or three months. And depending on the type of winter you get you may end up with high CSI or low CSI for a few weeks. You just don't know.

 

[Gary Davis]

Any effect of low CSI takes months or years to develop.

A pool is only closed for the winter for around 5 months. Any effect on the plaster by the CSI will only be for two or three months. And depending on the type of winter you get you may end up with high CSI or low CSI for a few weeks. You just don't know.

Thank you for that "months" or "years" length of time for a low CSI to aggressively "eat" the carbonates out of the plaster material.

Your number of "weeks" and "months" is the first time I've heard any length of time other than it takes a "long" time for aggressive water to suck something like fifty pounds of calcium carbonate [edit: chloride] out of your plaster pool (I just recently added fifty pounds of calcium carbonate [edit: chloride] for the winterization, so that's why I used that number).

I agree with you that the CSI is greatly affected by temperature which, if it fluctuates a lot during the winter, affects the CSI a lot during the winter.

But, when you eventually pour a hefty fifty pound bag of calcium carbonate [edit: chloride] into the pool over a period of weeks, your body (while holding that bag in your hands) gets an instant up-front whole hardy healthy appreciation for how much cold aggressive water can leach out of the plaster over time!

If what you're advising the OP is a temporary saturation imbalance is no big deal, I fully agree with you but temporary or not, the OP is asking about what happens when the TA is lowered (usually with muriatic acid), and what was well covered in the responses was how the pH is affected but I just wanted to let the OP know that the CSI is also affected when you lower the (carbonate) TA.

That's all I wanted to add.

My suggestion to the OP is that when you lower the (carbonate) TA by x ppm, you (often) need to raise the CH by 3x or 4x that (all other things being equal).
Of course, as you noted, the water temperature matters greatly, but notice that winter is coming so colder water makes the need to raise CH even greater (all other things being equal).

• Lowering (carbonate) TA (in and of itself) lowers the CSI
• Lowering Temperature (in and of itself) lowers the CSI

I only want the OP to consider that both of those equilibria indicate that he may need to take a LOOK at the CSI as a result of those two conditions.

It is when CSI drops below -0.6 and really below -1.0 for a length of time that it should be a concern.

I agree the CSI can fluctuate wildly (mostly due to temperature swings).

I usually try to keep the CSI within 0.3 on each end of a balanced zero, mostly due to how much the CSI changes with the temperature alone.
It's when it goes negative that I worry far more than when it goes positive (although I don't have a SWCG pool where a positive CSI matters more).

That means I worry more about balance when the water is cold than when it's hot (but I don't have a SWCG).

In a closed pool for the winter pH will rise and water temperature will fall which offset each other for the CSI.

Hmmmm....... certainly in winter the water temperature will fall which tends to make the water balance more aggressive (lower CSI).
And certainly the pH is a complex equilibria that is controlled by a multitude of factors...

One of those factors is the amount of dissolved carbon dioxide in the water, which, I would think would go the OPPOSITE of what you are suggesting.
That is, wouldn't a lower temperature cause MORE carbon dioxide to stay dissolved in the colder water - which would tend to LOWER pH (not raise it)?

Of course, when pH is being discussed, everything affects everything else, so the carbonate alkalinity would ALSO go up in colder water, and that alone would maybe balance the pH rise due to the carbon dioxide also becoming more soluble in the colder water.

I do not know which temperature-related solubility equilibria wins as the water gets colder.

• The pH lowers due to the colder water being more soluble for carbon dioxide?
• Or, pH rises due to the colder water being more soluble for carbonates?

It's complicated, and I admit I do NOT fully understand how this all plays - but I do know what I'm asking the OP to consider which is two things that didn't seem to be covered in this thread, which I only want to bring to the fore for the OP to consider.

1. Ask yourself WHY you're trying to lower TA (as the intended goal affects your calculations)
2. Ask yourself what happens to the CSI as you lower TA (as you may need to compensate to maintain balance)

 

[reggiehammond]

Any effect of low CSI takes months or years to develop.

Caveat being scale to SWCG if not managed negative - doesn't take long.

 

[JamesW]

My suggestion to the OP is that when you lower the (carbonate) TA by x ppm, you (often) need to raise the CH by 3x or 4x that (all other things being equal).

That's really not a good rule of thumb and it can be confusing when described this way.

(I just recently added fifty pounds of calcium carbonate for the winterization, so that's why I used that number).

It's calcium chloride.

 

[mgtfp]

I do not know which temperature-related solubility equilibria wins as the water gets colder.

• The pH lowers due to the colder water being more soluble for carbon dioxide?
• Or, pH rises due to the colder water being more soluble for carbonates?

pH rises naturally with falling temperatures because of the temperature dependency of the water dissociation constant.

Also keep in mind that CSI is only a measure for how far away from equilibrium dissolved calcium carbonate is, not how fast reactions are happening to get to equilibrium.

Reaction rates are accelerating exponentially with rising temperature (Arrhenius law). Therefore, a low CSI will be less critical at low temperatures compared to the same CSI at high temperatures, because it takes longer for calcium carbonate to dissolve.

 

[Gary Davis]

That's really not a good rule of thumb and it can be confusing when described this way.

It's not so much a rule of thumb as an almost unavoidable inevitability of good practices with respect to maintaining balance while adjusting balance.

However, I do agree in that the only goal of the ratio is to give you a good but only a rough idea of how much of each you're going to need.

• One down, three (or four) up!

That one-down:three-up ratio is only a rough estimate, where the actual amount depends on your testkit results.

For example, I use [extremely diluted] muriatic acid by the HASA case to lower my (carbonate) alkalinity in small increments of around 10 ppm and at the same time, I raised the calcium hardness in [extremely diluted] quantities by four times that in the beginning (i.e., by about 40 ppm CH) and then as I repeated the process later, also in [extremely diluted] amounts by about three times that (i.e., by about 30 ppm CH), and then as I approached target (carbonate) alkalinity, by about two times that (i.e., 20 ppm CH).

Notice what most people do is whatever the pool math calculator tells them to do, but some (most?) do it in one fell swoop.
The ratio helps you to break that one fell swoop into many fell swoops (what's a fell swoop anyway?)

It takes me, in the end, at least about a half dozen fell swoops to lower the (carbonate) alkalinity by a lot but keeping the saturation in balance the whole time.

It's calcium chloride.

Thank you for that correction, which I corrected (with a strikeout) in the original so as not to confuse others.
I much appreciate the correction and I provide a photo below of my 94% Calcium Chloride by way of hearty thankful agreement!

Notice in that photo how much concentrated acid and chlorine I stock up, by the way, as I buy it by the case as my fill water is extremely high in alkalinity and extremely low in calcium hardness, which is why I use the ratio to roughly estimate (actually, pretty accurately) the amount I'll need as I greatly dilute it prior to adding it to the pool.

The goal is to MAINTAIN the saturation level at the same time as I'm adjusting it (at roughly one down, three up).

1. First I add extremely diluted acid to lower (carbonate) alkalinity (which of course lowers the pH temporarily and which changes how pH rises)
2. Then I add a 3:1 or 4:1 ratio of extremely diluted Calcium Chloride to raise the CH which keeps the saturation index reasonably well balanced

One down, three up.

 

[mgtfp]

The goal is to MAINTAIN the saturation level at the same time as I'm adjusting it (at roughly one down, three up).

1. First I add extremely diluted acid to lower (carbonate) alkalinity (which of course lowers the pH temporarily and which changes how pH rises)
2. Then I add a 3:1 or 4:1 ratio of extremely diluted Calcium Chloride to raise the CH which keeps the saturation index reasonably well balanced

And what will you do in spring when the water gets warmer again? There is no magic potion to remove calcium from the water.

 

[Gary Davis]

And what will you do in spring when the water gets warmer again? There is no magic potion to remove calcium from the water.

Actually, there is magic involved.

I plan ahead thoroughly, where, put in the simplest terms, I swipe the right side of the pool math calculator in both temperature directions (i.e., all the way to 32 degrees left and all the way to about 85 degrees right) whenever I plan to adjust ANY of the half-dozen balance chemistry items (i.e., temperature, pH, carbonate alkalinity, calcium, cya, tds, & borate, if any).

It's not a kosher app for this forum [so I won't delve deeper] but it is wonderfully useful magic nonetheless in that you've maintained balance for ALL temperatures whenever you adjust balance at ANY temperature - and - along with using the one-down:three-up rule-of-thumb ratio with the multiple-step extremely-diluted-approach, you've maintained balance at every moment in time.

To me, that's magic.
With essentially four chemicals, I can maintain my pool sanitation and saturation at all times (without any temporary glitches).