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In a 280 gallon tub, lowering the TA by 20 ppm requires 1.92 ounces weight of dry acid (sodium bisulfate 93.2%). I assume the density of this dry acid is 1.44 g/ml (I measured that from a Spa Down product). This means that it takes 1.28 fluid ounces volume which is 7.7 teaspoons. I think you may be assuming a density of 1 since that would give 11.5 teaspoons.

The Taylor numbers are correct in that it takes 2.75 ounces weight of dry acid to lower the TA by 20 ppm in a 400 gallon tub. Again, it's the density that must be taken into account to convert from weight to volume.

Ok, gotcha. That's good to know. Although it would be nice if it mentioned that in the book.

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In Europe, people usually have scales since most everything is measured by weight and not volume. This is technically a much better way to go, both for cooking and for chemical additions to pools and spas. In the U.S. we tend to measure things by volume, so that's where the density of the substance becomes important. Unfortunately, density is not something that is consistent (except for solid blocks of a substance) since it's very dependent on the granularity of powdered products.

I've roughly determined the density of various pool chemicals and have that info built into my spreadsheet. 1 g/ml density (about the density of water) is equivalent to 0.96 fluid ounces per ounce weight (1.04 ounces weight per fluid ounce volume). This post gives the bulk density (which is what you purchase) of many common dry pool/spa chemicals, most of which I have measured myself.

Richard

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In Europe, people usually have scales since most everything is measured by weight and not volume. This is technically a much better way to go, both for cooking and for chemical additions to pools and spas. In the U.S. we tend to measure things by volume, so that's where the density of the substance becomes important. Unfortunately, density is not something that is consistent (except for solid blocks of a substance) since it's very dependent on the granularity of powdered products.

I've roughly determined the density of various pool chemicals and have that info built into my spreadsheet. 1 g/ml density (about the density of water) is equivalent to 0.96 fluid ounces per ounce weight (1.04 ounces weight per fluid ounce volume). This post gives the bulk density (which is what you purchase) of many common dry pool/spa chemicals, most of which I have measured myself.

Richard

Just to keep you updated (before I'm asking for advice again!!! )

Last night I put 1 TBS pH down around 5:00 and areated

2 people in tub from 7 until 10:40

at 8:30 I added 1 TBS Dichlor

checked at 10:30 pH 7.6, FC 8.0, TA 100

10:45 added 1 TBS pH down aerated 15 min.

Nov. 13 pH was 7.4, TA 100

I added 2 TBS Dichlor (the last two!!)

added 2TBS pH down aerated for olnly about 5 min. I thought the pH didn't need to go down, that is why. Am I correct here?

Later on tonight I was going to add the 'Omni Presence Plus' . Hopefully it is the same as the SpaGuard Plus.

The directions say this,"1. For initial application, broadcast 200g (approx. 13 tablespoons) of Omni Presence Plus per 1,000 litres of spa water, with the filter running. 2. On a weekly basis thereafter, 30 - 45 grams (2 - 3 tablespoons) of Omni Presence Plus per 1,000 litres to maintain optimal performance."

When they say "with the filter running", do they mean the jets?

Can you give me how much you think I should put in?

Also, I suppose I will just keep on slowly adding the pH down to reduce the TA? So far, as you can see, nothing seems to have happened to the TA.

By the way, just got the computer back!!

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In Europe, people usually have scales since most everything is measured by weight and not volume. This is technically a much better way to go, both for cooking and for chemical additions to pools and spas. In the U.S. we tend to measure things by volume, so that's where the density of the substance becomes important. Unfortunately, density is not something that is consistent (except for solid blocks of a substance) since it's very dependent on the granularity of powdered products.

I've roughly determined the density of various pool chemicals and have that info built into my spreadsheet. 1 g/ml density (about the density of water) is equivalent to 0.96 fluid ounces per ounce weight (1.04 ounces weight per fluid ounce volume). This post gives the bulk density (which is what you purchase) of many common dry pool/spa chemicals, most of which I have measured myself.

Richard

Just to keep you updated (before I'm asking for advice again!!! )

Last night I put 1 TBS pH down around 5:00 and areated

2 people in tub from 7 until 10:40

at 8:30 I added 1 TBS Dichlor

checked at 10:30 pH 7.6, FC 8.0, TA 100

10:45 added 1 TBS pH down aerated 15 min.

Nov. 13 pH was 7.4, TA 100

I added 2 TBS Dichlor (the last two!!)

added 2TBS pH down aerated for olnly about 5 min. I thought the pH didn't need to go down, that is why. Am I correct here?

Later on tonight I was going to add the 'Omni Presence Plus' . Hopefully it is the same as the SpaGuard Plus.

The directions say this,"1. For initial application, broadcast 200g (approx. 13 tablespoons) of Omni Presence Plus per 1,000 litres of spa water, with the filter running. 2. On a weekly basis thereafter, 30 - 45 grams (2 - 3 tablespoons) of Omni Presence Plus per 1,000 litres to maintain optimal performance."

When they say "with the filter running", do they mean the jets?

Can you give me how much you think I should put in?

Also, I suppose I will just keep on slowly adding the pH down to reduce the TA? So far, as you can see, nothing seems to have happened to the TA.

By the way, just got the computer back!!

oops, 3 people in tub...2 sweaty men, and moi! LOL

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Nov. 13 pH was 7.4, TA 100

I added 2 TBS Dichlor (the last two!!)

added 2TBS pH down aerated for olnly about 5 min. I thought the pH didn't need to go down, that is why. Am I correct here?

Later on tonight I was going to add the 'Omni Presence Plus' . Hopefully it is the same as the SpaGuard Plus.

The directions say this,"1. For initial application, broadcast 200g (approx. 13 tablespoons) of Omni Presence Plus per 1,000 litres of spa water, with the filter running. 2. On a weekly basis thereafter, 30 - 45 grams (2 - 3 tablespoons) of Omni Presence Plus per 1,000 litres to maintain optimal performance."

When they say "with the filter running", do they mean the jets?

Can you give me how much you think I should put in?

Also, I suppose I will just keep on slowly adding the pH down to reduce the TA? So far, as you can see, nothing seems to have happened to the TA.

Laura,

The reason for adding pH down was to lower the TA since pH down will lower BOTH pH AND TA while aeration only increases pH with no change in TA. So by doing both acid addition and aeration, the TA gets lowered.

You probably won't need to add the Omni Presence Plus every week -- it doesn't break down and I don't think you have a lot of splash out (evaporation doesn't remove the product). I can't find anything on the web about this specific product. Is their an ingredients list on it and if so, what does it say?

"with the filter running" means having at least the circulation filter on. You don't have to have the jets on. Your spa should have a mode where the water is circulated even if the jets are not on. If you can't figure out how to do that, then run with the jets on but I'd add the product near and not in front of a jet since you don't want things to splash out (in your face, etc.).

If the Omni Presence Plus product is mostly Boric Acid, then 200 grams per 1000 liters would raise the borates level by 35 ppm. For your 380 gallon spa and to get to 50 ppm Borates, I would add 14-1/2 ounces weight or a little more than 8 fluid ounces volume (that's one cup which is 16 tablespoons). You say that 200 grams is approximately 13 tablespoons which would be a density of 1.04 g/ml -- was the "approximately 13 tablespoons" something they said or something you estimated or something you actually weighed? The density of Boric Acid is more like 1.66 g/ml -- Borax is closer to 1.0 g/ml. So if you have a scale (say, a postage scale), weigh 1 cup or some other large amount of the product. I would expect 1 cup to weigh about 14 ounces (about 410 grams). If it instead weighs closer to 8 ounces (about 225 grams), then the product is more likely to be Borax and may not be pH balanced.

Richard

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Nov. 13 pH was 7.4, TA 100

I added 2 TBS Dichlor (the last two!!)

added 2TBS pH down aerated for olnly about 5 min. I thought the pH didn't need to go down, that is why. Am I correct here?

Later on tonight I was going to add the 'Omni Presence Plus' . Hopefully it is the same as the SpaGuard Plus.

The directions say this,"1. For initial application, broadcast 200g (approx. 13 tablespoons) of Omni Presence Plus per 1,000 litres of spa water, with the filter running. 2. On a weekly basis thereafter, 30 - 45 grams (2 - 3 tablespoons) of Omni Presence Plus per 1,000 litres to maintain optimal performance."

When they say "with the filter running", do they mean the jets?

Can you give me how much you think I should put in?

Also, I suppose I will just keep on slowly adding the pH down to reduce the TA? So far, as you can see, nothing seems to have happened to the TA.

Laura,

The reason for adding pH down was to lower the TA since pH down will lower BOTH pH AND TA while aeration only increases pH with no change in TA. So by doing both acid addition and aeration, the TA gets lowered.

You probably won't need to add the Omni Presence Plus every week -- it doesn't break down and I don't think you have a lot of splash out (evaporation doesn't remove the product). I can't find anything on the web about this specific product. Is their an ingredients list on it and if so, what does it say?

"with the filter running" means having at least the circulation filter on. You don't have to have the jets on. Your spa should have a mode where the water is circulated even if the jets are not on. If you can't figure out how to do that, then run with the jets on but I'd add the product near and not in front of a jet since you don't want things to splash out (in your face, etc.).

If the Omni Presence Plus product is mostly Boric Acid, then 200 grams per 1000 liters would raise the borates level by 35 ppm. For your 380 gallon spa and to get to 50 ppm Borates, I would add 14-1/2 ounces weight or a little more than 8 fluid ounces volume (that's one cup which is 16 tablespoons). You say that 200 grams is approximately 13 tablespoons which would be a density of 1.04 g/ml -- was the "approximately 13 tablespoons" something they said or something you estimated or something you actually weighed? The density of Boric Acid is more like 1.66 g/ml -- Borax is closer to 1.0 g/ml. So if you have a scale (say, a postage scale), weigh 1 cup or some other large amount of the product. I would expect 1 cup to weigh about 14 ounces (about 410 grams). If it instead weighs closer to 8 ounces (about 225 grams), then the product is more likely to be Borax and may not be pH balanced.

Richard

I typed the directions that were on the label. It also say the is a " Mulit-Functional water enhancer with corroision inhititors.

Makes water feel soft and silky. Enhances bather comfort. Improves water clarity. Protects metal surfaces and equipment.Does not affect pH and improves water comfort."

It does not however list any ingredients. I was assured by the spa store that it is the same as the SpaGuard product.

I started with the Purox last night. We had 4 in for 5 hours. Great fun. I added 1/3 cup in during the soak, and another 1/3 after, with 2 more TBS pH down.

This morning I added another 1/3 cup Purox.

Just now, I added 3 TBS pH down, along with the aeration, and then 7 TBS of the Omni Presence Plus (brings it up to 16 TBS in total)

The FC according to the test strip seems fine. I am going to re-test everything with the Taylor Kit a little later on today.

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Nov. 13 pH was 7.4, TA 100

I added 2 TBS Dichlor (the last two!!)

added 2TBS pH down aerated for olnly about 5 min. I thought the pH didn't need to go down, that is why. Am I correct here?

Later on tonight I was going to add the 'Omni Presence Plus' . Hopefully it is the same as the SpaGuard Plus.

The directions say this,"1. For initial application, broadcast 200g (approx. 13 tablespoons) of Omni Presence Plus per 1,000 litres of spa water, with the filter running. 2. On a weekly basis thereafter, 30 - 45 grams (2 - 3 tablespoons) of Omni Presence Plus per 1,000 litres to maintain optimal performance."

When they say "with the filter running", do they mean the jets?

Can you give me how much you think I should put in?

Also, I suppose I will just keep on slowly adding the pH down to reduce the TA? So far, as you can see, nothing seems to have happened to the TA.

Laura,

The reason for adding pH down was to lower the TA since pH down will lower BOTH pH AND TA while aeration only increases pH with no change in TA. So by doing both acid addition and aeration, the TA gets lowered.

You probably won't need to add the Omni Presence Plus every week -- it doesn't break down and I don't think you have a lot of splash out (evaporation doesn't remove the product). I can't find anything on the web about this specific product. Is their an ingredients list on it and if so, what does it say?

"with the filter running" means having at least the circulation filter on. You don't have to have the jets on. Your spa should have a mode where the water is circulated even if the jets are not on. If you can't figure out how to do that, then run with the jets on but I'd add the product near and not in front of a jet since you don't want things to splash out (in your face, etc.).

If the Omni Presence Plus product is mostly Boric Acid, then 200 grams per 1000 liters would raise the borates level by 35 ppm. For your 380 gallon spa and to get to 50 ppm Borates, I would add 14-1/2 ounces weight or a little more than 8 fluid ounces volume (that's one cup which is 16 tablespoons). You say that 200 grams is approximately 13 tablespoons which would be a density of 1.04 g/ml -- was the "approximately 13 tablespoons" something they said or something you estimated or something you actually weighed? The density of Boric Acid is more like 1.66 g/ml -- Borax is closer to 1.0 g/ml. So if you have a scale (say, a postage scale), weigh 1 cup or some other large amount of the product. I would expect 1 cup to weigh about 14 ounces (about 410 grams). If it instead weighs closer to 8 ounces (about 225 grams), then the product is more likely to be Borax and may not be pH balanced.

Richard

I typed the directions that were on the label. It also say the is a " Mulit-Functional water enhancer with corroision inhititors.

Makes water feel soft and silky. Enhances bather comfort. Improves water clarity. Protects metal surfaces and equipment.Does not affect pH and improves water comfort."

It does not however list any ingredients. I was assured by the spa store that it is the same as the SpaGuard product.

I started with the Purox last night. We had 4 in for 5 hours. Great fun. I added 1/3 cup in during the soak, and another 1/3 after, with 2 more TBS pH down.

This morning I added another 1/3 cup Purox.

Just now, I added 3 TBS pH down, along with the aeration, and then 7 TBS of the Omni Presence Plus (brings it up to 16 TBS in total)

The FC according to the test strip seems fine. I am going to re-test everything with the Taylor Kit a little later on today.

hmmmm Here are the results. I am not sure if you are going to like them much:

pH 7.0 (still aerating) about 20 min so far.

TA 50

CH 200

CYA 35

FC 5.5

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hmmmm Here are the results. I am not sure if you are going to like them much:

pH 7.0 (still aerating) about 20 min so far.

TA 50

CH 200

CYA 35

FC 5.5

I wouldn't add anymore pH Down. If you can get your pH to 7.6-7.8 by aerating you should be ok.

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Laura,

Yup. You've added enough acid; more than you should have. In fact, in my post here I said you'd need a cumulative total of 10 teaspoons to get the TA from 100 to 80. In this post you said you added 1 TBS + 1 TBS + 2 TBS so that's 4 TBS and then in this post you say you added another 3 TBS so that's a total of 7 TBS of dry acid. That's 21 teaspoons (there are 3 teaspoons in a tablespoon and 2 tablespoons in a fluid ounce) or more than double the amount of acid I suggested. So instead of lowering your TA by 20 ppm from 100 to 80, you lowered it by 50 ppm from 100 to 50 (it's probably more like 40 ppm, but with some measurement error or your dry acid is a little more dense than I assumed).

Just aerate the water which will get your pH up a bit closer to 7.5. And please try to pay attention to the quantities so you don't overdose in the future.

Richard

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Chem Geek,

I just changed my water, I'm debating on how much Calcium to use. Before this refill, I had my TA at 60 ppm, and my pH was locked at 7.6-7.8. However with CH at 150 ppm, that's a little acidic. What would be the issue with having a higher CH i.e. 200-250?

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Chem Geek,

I just changed my water, I'm debating on how much Calcium to use. Before this refill, I had my TA at 60 ppm, and my pH was locked at 7.6-7.8. However with CH at 150 ppm, that's a little acidic. What would be the issue with having a higher CH i.e. 200-250?

AAHH crap....I did think it wasTBS. I will surely be more cautious. Thank you both for your help!

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Chem Geek,

I just changed my water, I'm debating on how much Calcium to use. Before this refill, I had my TA at 60 ppm, and my pH was locked at 7.6-7.8. However with CH at 150 ppm, that's a little acidic. What would be the issue with having a higher CH i.e. 200-250?

At a 100F temperature, and with 50 ppm Borates and 30 ppm CYA, the saturation index is from -0.32 to -0.18 so is on the corrosive/dissolving side. So IF you keep your TA at 60 and your pH in the 7.6-7.8 range, then a CH of 200-250 would be better. The 50 ppm Borates contribute around 9 ppm to the TA at this higher temperature (at 80F, it only adds around 6 ppm to TA). So between the Borates and the CYA, the carbonate alkalinity is 40 (at pH 7.6) to 35 (at pH 7.8). The good news with that is greater pH stability, but it does mean you can compensate for these low carbonates with higher calcium hardness.

This just points out that when having higher CYA or having Borates, one should probably not go below 60 ppm in TA. The 50 ppm TA floor I sometimes refer to would be with no Borates and the lower 20 ppm CYA level.

Richard

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Chem Geek,

I just changed my water, I'm debating on how much Calcium to use. Before this refill, I had my TA at 60 ppm, and my pH was locked at 7.6-7.8. However with CH at 150 ppm, that's a little acidic. What would be the issue with having a higher CH i.e. 200-250?

At a 100F temperature, and with 50 ppm Borates and 30 ppm CYA, the saturation index is from -0.32 to -0.18 so is on the corrosive/dissolving side. So IF you keep your TA at 60 and your pH in the 7.6-7.8 range, then a CH of 200-250 would be better. The 50 ppm Borates contribute around 9 ppm to the TA at this higher temperature (at 80F, it only adds around 6 ppm to TA). So between the Borates and the CYA, the carbonate alkalinity is 40 (at pH 7.6) to 35 (at pH 7.8). The good news with that is greater pH stability, but it does mean you can compensate for these low carbonates with higher calcium hardness.

This just points out that when having higher CYA or having Borates, one should probably not go below 60 ppm in TA. The 50 ppm TA floor I sometimes refer to would be with no Borates and the lower 20 ppm CYA level.

Richard

So Richard, should I consider raising my TA to 60ppm?

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So Richard, should I consider raising my TA to 60ppm?

Why don't you wait until you've finished the chemical additions including Omni Presence Plus and have you using Purox. We can then see what sort of pH stability you have and get a better sense for your numbers. Then, we may increase TA a little and possibly CH as well, but this isn't urgent. Having these numbers somewhat low isn't going to cause damage quickly. It's when people have virtually no TA and let their pH crash (i.e. drop precipitously) that problems can occur more quickly.

So enjoy the tub, test regularly, and report how things are going. We can then see how things look for you day-to-day.

If this site continues to get spam as it has recently, y'all might consider posting to the Spa / Hot Tub Care section at Trouble Free Pool.

Richard

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At a 100F temperature, and with 50 ppm Borates and 30 ppm CYA, the saturation index is from -0.32 to -0.18 so is on the corrosive/dissolving side. So IF you keep your TA at 60 and your pH in the 7.6-7.8 range, then a CH of 200-250 would be better. The 50 ppm Borates contribute around 9 ppm to the TA at this higher temperature (at 80F, it only adds around 6 ppm to TA). So between the Borates and the CYA, the carbonate alkalinity is 40 (at pH 7.6) to 35 (at pH 7.8). The good news with that is greater pH stability, but it does mean you can compensate for these low carbonates with higher calcium hardness.

This just points out that when having higher CYA or having Borates, one should probably not go below 60 ppm in TA. The 50 ppm TA floor I sometimes refer to would be with no Borates and the lower 20 ppm CYA level.

Richard

I may raise my CH then. I found when my TA was ~60, my pH was rock solid. However, if I kept it at 70 or higher, my pH would drift up. So the only other variable that can be changed to bring up SI is Calcium. BTW, is there any downside to have really high CH, like 300-400, assuming the SI is zero?

Also, I see Salt plays a role. As Salt rises, SI goes down. How much Salt is being added/created in our tubs?

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Another quick question. If someone were to continually add acid (i.e. once a week) because of pH drift, wouldn't their TA slowly drop over time, or is there something else going on?

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I may raise my CH then. I found when my TA was ~60, my pH was rock solid. However, if I kept it at 70 or higher, my pH would drift up. So the only other variable that can be changed to bring up SI is Calcium. BTW, is there any downside to have really high CH, like 300-400, assuming the SI is zero?

Also, I see Salt plays a role. As Salt rises, SI goes down. How much Salt is being created in our tubs?

There is no downside to the higher calcium levels if the other parameters are such that the saturation index is near zero. In fact, with regards to plaster protection, a high CH with lower TA is theoretically better, not for preventing dissolving of calcium carbonate, but for preventing dissolving of calcium oxide which is bound in plaster as calcium silicate hydrate (3CaO•SiO2•4H2O). The reaction is as follows:

CaO + CO2 --> Ca2+ + CO32- + heat

Calcium Oxide + Carbon Dioxide ---> Calcium Ion + Carbonate Ion + heat

Clearly, the right hand side product of calcium and carbonate is maximized at saturation so any saturation index near zero has the product on the right be maximized. However, notice that on the left hand side there is carbon dioxide. To reduce the rate of this reaction, one wants to not only maximize the products, but also to minimize the carbon dioxide and that is done either through a lower TA or a higher pH or both. Since the pH needs to be somewhat near 7.5 to minimize eye irritation (among other things), this means that a lower TA is better. In order to keep the water saturated with calcium carbonate, the CH must be higher. That is why I said that theoretically a lower TA with a higher CH is better, at least in preventing plaster/grout/concrete/gunite degradation. By the way, when one refers to plaster in pools, it's really cement plaster (as opposed to plaster of Paris which is based on calcium sulfate, not calcium carbonate).

As for salt, for every 10 ppm FC added by bleach (or chlorinating liquid or Lithium Hypochlorite powder), it also increases salt by 16 ppm (8 ppm upon addition and another 8 ppm when the chlorine gets used up and converted to chloride). So if you have one person soaking for about a half-hour every day, then perhaps you are adding 4 ppm FC in 350 gallons so that comes to about 200 ppm salt per month. So even after 6 months, you've only added around 1200 ppm salt and you probably start out with around 400-500 ppm TDS (700-800 ppm TDS if you have 50 ppm Borates). This extra salt lowers the saturation index by about 0.13 so not too much. The easiest way to handle this is to target a slightly higher pH by 0.1 unit during the second half of your usage, assuming you are going for 6 months at the bather load I indicated. The standard Water Replacement Index (WRI) for one person soaking (presumably for a 20-30 minute soak) in a 350 gallon tub is almost 4 months. Using Dichlor and then bleach perhaps lets you go longer so in general if this is doubled (perhaps not in time, but in bather load) then that's 1600 ppm extra salt or a change in saturation index of about 0.16 -- still not very much.

Richard

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Another quick question. If someone were to continually add acid (i.e. once a week) because of pH drift, wouldn't their TA slowly drop over time, or is there something else going on?

Yes, their TA would slowly drop over time since you are essentially doing the TA lowering procedure very slowly over time. The pH drift is presumably a rise due to outgassing of carbon dioxide -- or if the acid is being added regularly as with Dichlor or MPS, then the pH may be seen to be stable or even going down, but carbon dioxide outgassing is still occurring. The TA will drop by an amount predicted solely by the amount of acid you add (and spa volume), assuming no pH Up or Alkalinity Up product is added. So in situations where Dichlor or MPS is used or when bleach is used and acid is added, if the pH is kept stable then the TA slowly drops.

So when using acid to control pH, one needs to periodically monitor the TA level to make sure it doesn't drop too much. With your numbers, including Borates, going from a pH of 7.8 to 7.6 takes (in 350 gallons) 1.3 fluid ounces (about 8 teaspoons) of Muriatic Acid (31.45% hydrochloric acid) or 0.76 ounces weight (about 1 tablespoon) of dry acid (93.2% sodium bisulfate) and results in a drop in TA of 6.2 ppm.

Richard

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As I mentioned when my TA was ~60 I had my pH stable between 7.6 and 7.8 for weeks without ever going over 7.8. I wonder if it's possible to get pH to hover between 7.4 and 7.6 by lowering TA to ~50. If I did, I'd have to have ~400 ppm CH to counter balance it. I feel a little nervous about putting that much calcium in my tub though, because once you add it, you can't take it out without draining.

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So Richard, should I consider raising my TA to 60ppm?

Why don't you wait until you've finished the chemical additions including Omni Presence Plus and have you using Purox. We can then see what sort of pH stability you have and get a better sense for your numbers. Then, we may increase TA a little and possibly CH as well, but this isn't urgent. Having these numbers somewhat low isn't going to cause damage quickly. It's when people have virtually no TA and let their pH crash (i.e. drop precipitously) that problems can occur more quickly.

So enjoy the tub, test regularly, and report how things are going. We can then see how things look for you day-to-day.

If this site continues to get spam as it has recently, y'all might consider posting to the Spa / Hot Tub Care section at Trouble Free Pool.

Richard

I just can't thank you enough (again) for all of your time and help. I've just got to tell you that you have no idea how much your help (and Nitro's too ) means to me. I am learning so much and I'm actually enjoying it. I promise that I will be more dedicated to the exact measurments. You might not like this, but I did add one teaspoon of pH up just to help me out, as the areating for over an hour did bring up the pH, but not enough IMHO.

It's funny that you mentioned another site as I was going to ask you about that. Would you rather I started posting my test results there instead of here? This site does make me nervous after last weekend.

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Another quick question. If someone were to continually add acid (i.e. once a week) because of pH drift, wouldn't their TA slowly drop over time, or is there something else going on?

Yes, their TA would slowly drop over time since you are essentially doing the TA lowering procedure very slowly over time. The pH drift is presumably a rise due to outgassing of carbon dioxide -- or if the acid is being added regularly as with Dichlor or MPS, then the pH may be seen to be stable or even going down, but carbon dioxide outgassing is still occurring. The TA will drop by an amount predicted solely by the amount of acid you add (and spa volume), assuming no pH Up or Alkalinity Up product is added. So in situations where Dichlor or MPS is used or when bleach is used and acid is added, if the pH is kept stable then the TA slowly drops.

So when using acid to control pH, one needs to periodically monitor the TA level to make sure it doesn't drop too much. With your numbers, including Borates, going from a pH of 7.8 to 7.6 takes (in 350 gallons) 1.3 fluid ounces (about 8 teaspoons) of Muriatic Acid (31.45% hydrochloric acid) or 0.76 ounces weight (about 1 tablespoon) of dry acid (93.2% sodium bisulfate) and results in a drop in TA of 6.2 ppm.

Richard

I guess my question is: is it possible to STOP pH drift by lowering TA to some value? OR, will pH drift up from aeration no matter how low TA is?

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I guess my question is: is it possible to STOP pH drift by lowering TA to some value? OR, will pH drift up from aeration no matter how low TA is?

The upward drift of pH, ignoring any chemical additions that aren't net pH neutral, will occur from the outgassing of carbon dioxide until it reaches equilibrium with the air. At a pH of 7.5, that's a carbonate alkalinity of 9 ppm. At a pH of 7.8, that's a carbonate alkalinity of 18 ppm. With 30 ppm CYA and 50 ppm Borates, this translates roughly into 24 ppm TA and 38 ppm TA, respectively (and this is with no chlorine in the water -- the chlorine has some alkalinity as well, though it's relatively small). However, from a practical point of view, the outgassing slows down as one approaches these low TA levels which is what you have noticed. You can see the relationship between TA and pH in terms of outgassing. This chart shows the relative outgas rates as a function of pH and TA assuming such rates are solely due to the degree the equilibrium is out of balance. In reality, there is a non-linear (square) relationship between outgassing rates and TA (presumably from facilitated transport, according to Wojtowicz) so the effect of TA on the rate of pH rise is noticeable -- again, something you have noticed.

In a spa, there is really nothing wrong with targeting a pH of 7.7 or 7.8 since you do not intend to dunk your face into the water. The pH of 7.5 is mostly for having the least effect on one's eyes. There is also somewhat lower active chlorine amounts at higher pH, but as I've shown in other posts with the graphs of such relationship, there isn't a huge change when CYA is present since CYA buffers active chlorine to some degree. Also, you can't have such a low carbonate alkalinity because it would require way too much calcium.

So if I were you, I wouldn't push it any further and just enjoy the stable situation you have now. You really want a decent amount of that carbonate buffer in the water in case you accidentally add too much acid. The Borates buffer will run out rather early against a lowering of pH, the CYA buffer is there but not as strong as the carbonate buffer system. Also, if you had a pH of 7.5 and a TA of 24 ppm, there is NO amount of calcium that would get you above a saturation index of around -0.4 (since higher CH not only increases calcium, but increases TDS or ionic strength). Basically, as you go lower in TA, things fall apart quite rapidly as you get closer to that equilibrium carbonate alkalinity limit. For saturation with a TA of 40 ppm (and pH of 7.5), you'd need about 1200 ppm CH. At a TA of 50 ppm, it's 700 ppm. At a TA of 60 ppm, it's 500 ppm. So having a somewhat higher pH target and a reasonable TA lets you also have a reasonable CH as well.

Richard

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I'll probably up the CH to 200 for now. That will keep it well balanced with TA of 60 and pH of 7.6-7.8. If I have to lower TA to 50 in order to keep the pH in line, I'll raise the CH to 250. I may raise it every month anyway to counter the Salt.

BTW, I noticed a MAJOR difference in the appearence of the water on this refill. My old water was definitely sluggish, and it's only been 2 months. It's amazing how much fresh water makes a difference. Hopefully, I'll get at least 4 months out of this fill. We get pretty long winters here in Chicago.

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I'll probably up the CH to 200 for now. That will keep it well balanced with TA of 60 and pH of 7.6-7.8. If I have to lower TA to 50 in order to keep the pH in line, I'll raise the CH to 250. I may raise it every month anyway to counter the Salt.

BTW, I noticed a MAJOR difference in the appearence of the water on this refill. My old water was definitely sluggish, and it's only been 2 months. It's amazing how much fresh water makes a difference. Hopefully, I'll get at least 4 months out of this fill. We get pretty long winters here in Chicago.

So was this past 2 months Dichlor then bleach or did you start out with it as Dichlor only? Definitely keep us posted on how it goes from here -- most people who've tried Dichlor then bleach get about double the length of time before water replacement and their water isn't as noticeably funky either. Of course, it depends on how clean one is when using the tub since some oils and lotions will build up even using chlorine properly.

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I just can't thank you enough (again) for all of your time and help. I've just got to tell you that you have no idea how much your help (and Nitro's too ) means to me. I am learning so much and I'm actually enjoying it. I promise that I will be more dedicated to the exact measurments. You might not like this, but I did add one teaspoon of pH up just to help me out, as the areating for over an hour did bring up the pH, but not enough IMHO.

It's funny that you mentioned another site as I was going to ask you about that. Would you rather I started posting my test results there instead of here? This site does make me nervous after last weekend.

You are most welcome. You can continue to post here for now, but my "home" is really at Trouble Free Pool (TFP) and if this site continues with the spam posts I'll probably be leaving. If you want to move to TFP you are certainly welcome to and there are others there who can help you -- Nitro has signed up over there and waterbear has always been there (he used to post here more frequently).

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