Where Does One Obtain Dry Acid (sodium Bisulfate)? - Hot Tub Water Chemistry - Pool and Spa Forum

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Where Does One Obtain Dry Acid (sodium Bisulfate)?


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#1 zoetman

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Posted 21 December 2007 - 11:17 PM

where do I obtain dry acid (sodium bisulfate)? Rather than pay the spa store for their overpriced version.
Also, as I am new at this, please tell me if I'm doing this right: Okay, I'm using chlorine, borax/baking soda to increase Ph/alklinity as needed. Plus I'm using PH decreaser right now. Plus MPS. I don't understand what the MPS is for? I know it's a sanitizer but isn't that what the chlorine is for? Please clarify. Thanks a bunch. If MPS is needed, is there any generic source? thanks again, zoetman

#2 chem geek

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Posted 22 December 2007 - 12:42 AM

Though I know you can buy Muriatic Acid at hardware stores and can get half-strength versions that don't fume as much, I don't know where you can get generic dry acid. If you are careful with the Muriatic Acid, you can use that instead, but I would dilute it before using it and only add it very, very slowly over a return flow. Both Muriatic Acid and dry acid are very strong.

MPS is NOT a sanitizer. It is an oxidizer whereas chlorine is a sanitizer and also an oxidizer. The main reason to use MPS is that it oxidizes organics better than chlorine and with less side effects, but it isn't always necessary. One can sometimes just use chlorine alone (certainly that is true in pools -- for spas with the heavier bather load it's not always true). I don't know of any generic source for MPS.

Richard

#3 zoetman

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Posted 22 December 2007 - 11:01 AM

QUOTE(chem geek @ Dec 22 2007, 12:42 AM) <{POST_SNAPBACK}>
Though I know you can buy Muriatic Acid at hardware stores and can get half-strength versions that don't fume as much, I don't know where you can get generic dry acid. If you are careful with the Muriatic Acid, you can use that instead, but I would dilute it before using it and only add it very, very slowly over a return flow. Both Muriatic Acid and dry acid are very strong.

MPS is NOT a sanitizer. It is an oxidizer whereas chlorine is a sanitizer and also an oxidizer. The main reason to use MPS is that it oxidizes organics better than chlorine and with less side effects, but it isn't always necessary. One can sometimes just use chlorine alone (certainly that is true in pools -- for spas with the heavier bather load it's not always true). I don't know of any generic source for MPS.

Richard



thanks Richard. How much muriatic acid would I start with - like a tablespoon diluted?

Beverly

#4 chem geek

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Posted 22 December 2007 - 12:58 PM

Beverly,

You use approximately the same volume of Muriatic Acid (full strength 31.45% Hydrochloric acid -- use twice as much if you use half-strength) as you do Dry Acid. The dry acid is a little denser so that same volume weighs a bit more, but in terms of volume they are very similar. As for how much, that depends on what you are trying to do in terms of pH and what your current TA is. For example, adding one tablespoon of Muriatic Acid to 350 gallons starting at a pH of 7.7 and TA of 100 will lower the pH to 7.33 so the amount you are talking about sounds about right.

So you can take a cup or container of spa water, add the tablespoon of acid to it, then slowly pour that over a return flow. Obviously use a container that isn't metal -- glass is perfect, certain plastics are OK (the acid comes in a plastic container, for example).

By the way, acids will last seemingly forever. However, I would only store the Muriatic Acid in a well-ventilated area away from metal objects and be sure to TIGHTLY close the cap. I've heard of people keeping acid in the garage and their bikes near the acid rusted. If you have a well-ventilated shed outside, then that would be fine -- the freezing point for full strength Muriatic Acid is -51F so unless you are in the Artic, you have nothing to worry about (even half strength would freeze at -5F so unless you have sustained sub-zero temperatures outdoor storage should be OK).

Oh, and one more thing. You probably won't need to use any pH decreaser or certainly not very much if you lower the TA level of your spa. High TA plus aeration leads to pH rise. You can lower the TA by following the procedure in this post.

Richard

#5 chem geek

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Posted 23 December 2007 - 03:23 PM

Beverly,

I want to refer you to this post from waterbear where he does not normally recommend using Muriatic Acid since it is harder to deal with. I agree and you've noticed from my previous post the downsides to Muriatic Acid in terms of its fuming (though half-strength solutions aren't as bad) and the difficulty of measuring smaller amounts of liquid compared to dry granules. It's still up to you, but with Muriatic Acid you do have to be more careful.

If you lower the TA of your spa, then you should not need to add acid very often so the higher price of dry acid shouldn't be as much of an issue. Again, you can go either way, but I wanted you to be as informed as possible in making the decision.

Richard

#6 zoetman

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Posted 23 December 2007 - 06:12 PM

QUOTE(chem geek @ Dec 23 2007, 03:23 PM) <{POST_SNAPBACK}>
Beverly,

I want to refer you to this post from waterbear where he does not normally recommend using Muriatic Acid since it is harder to deal with. I agree and you've noticed from my previous post the downsides to Muriatic Acid in terms of its fuming (though half-strength solutions aren't as bad) and the difficulty of measuring smaller amounts of liquid compared to dry granules. It's still up to you, but with Muriatic Acid you do have to be more careful.

If you lower the TA of your spa, then you should not need to add acid very often so the higher price of dry acid shouldn't be as much of an issue. Again, you can go either way, but I wanted you to be as informed as possible in making the decision.

Richard



thanks Richard. I think I'll stick with the dry acid. I also had a question. You( or someone) mentions that you don't necessarily need MPS with a bromine system. What about with a chlorine system (dichlor). My spa is indoors. Thanks Beverly

#7 chem geek

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Posted 23 December 2007 - 08:25 PM

Basically, in a bromine system you have to have some sort of oxidizer to regenerate the bromine. In some bromine systems where you just have bromide in the spa, then you add chlorine to regenerate the bromine. In other bromine systems that use slow-dissolving bromine tablet feeders, they provide both bromide and chlorine so regenerate the bromine on-the-fly.

In both bromine and chlorine systems, there may be a need for additional shocking, perhaps weekly, to oxidize the organics that can build up. This may or may not be necessary depending on the bather load (i.e. how much the spa gets used; its water volume; etc.). One can do the shocking with either chlorine or MPS. Each has its pros and cons. The chlorine is less expensive but requires you to wait for the chlorine level to drop before re-entering the spa, but in a spa the chlorine level often drops fairly quickly so the next day is usually OK to get back in.

If you use MPS, which is more expensive, then it can result in somewhat lower chlorine usage as it will oxidize organics instead of chlorine having to do this. It will also reduce disinfection by-products so may reduce some smell. However, some people are skin sensitive to MPS and a regular regimen of chlorine-only dosing usually works reasonably well.

The simplest approach is to start with chlorine alone, adding enough chlorine when you get out of the spa so that when you next get in you measure at least some Free Chlorine (FC) and minimal (< 0.5 ppm) Combined Chlorine (CC). If you find that the chlorine demand is high or that CC tends to form, then you can try shocking with chlorine to 10 ppm FC or so once a week. If that doesn't work to prevent CCs, then try using MPS instead, at first once a week and if necessary more frequently than that (at relatively lower doses if done more frequently). There is no right answer here as there is more than one way to manage a spa. The most important thing is to ensure that there is disinfectant in the spa at all times. The rest is more of a personal choice of regimen.

Remember that for chlorine, you only want to use Dichlor for a short time (around 1-2 weeks) getting to 4 ppm FC each time you get out of the spa and then you want to switch to unscented bleach.

Richard

#8 zoetman

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Posted 23 December 2007 - 10:21 PM

QUOTE(chem geek @ Dec 23 2007, 08:25 PM) <{POST_SNAPBACK}>
Basically, in a bromine system you have to have some sort of oxidizer to regenerate the bromine. In some bromine systems where you just have bromide in the spa, then you add chlorine to regenerate the bromine. In other bromine systems that use slow-dissolving bromine tablet feeders, they provide both bromide and chlorine so regenerate the bromine on-the-fly.

In both bromine and chlorine systems, there may be a need for additional shocking, perhaps weekly, to oxidize the organics that can build up. This may or may not be necessary depending on the bather load (i.e. how much the spa gets used; its water volume; etc.). One can do the shocking with either chlorine or MPS. Each has its pros and cons. The chlorine is less expensive but requires you to wait for the chlorine level to drop before re-entering the spa, but in a spa the chlorine level often drops fairly quickly so the next day is usually OK to get back in.

If you use MPS, which is more expensive, then it can result in somewhat lower chlorine usage as it will oxidize organics instead of chlorine having to do this. It will also reduce disinfection by-products so may reduce some smell. However, some people are skin sensitive to MPS and a regular regimen of chlorine-only dosing usually works reasonably well.

The simplest approach is to start with chlorine alone, adding enough chlorine when you get out of the spa so that when you next get in you measure at least some Free Chlorine (FC) and minimal (< 0.5 ppm) Combined Chlorine (CC). If you find that the chlorine demand is high or that CC tends to form, then you can try shocking with chlorine to 10 ppm FC or so once a week. If that doesn't work to prevent CCs, then try using MPS instead, at first once a week and if necessary more frequently than that (at relatively lower doses if done more frequently). There is no right answer here as there is more than one way to manage a spa. The most important thing is to ensure that there is disinfectant in the spa at all times. The rest is more of a personal choice of regimen.

Remember that for chlorine, you only want to use Dichlor for a short time (around 1-2 weeks) getting to 4 ppm FC each time you get out of the spa and then you want to switch to unscented bleach.

Richard

Thanks Richard, your help is invaluable. When I go to the spa store, they just say, buy this, buy that.

beverly



#9 waterbear

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Posted 23 December 2007 - 11:31 PM

QUOTE(zoetman @ Dec 23 2007, 09:12 PM) <{POST_SNAPBACK}>
thanks Richard. I think I'll stick with the dry acid. I also had a question. You( or someone) mentions that you don't necessarily need MPS with a bromine system. What about with a chlorine system (dichlor). My spa is indoors. Thanks Beverly

Actually, it was me. In a bromine system MPS is generally used as an oxidizer but is wrongly referred to as a shock. Chlorine is just as effective and quite a bit less expensive for this purpose with bromine. MPS has no advantages in a bromine system since either MPS or chlorine will cause the bromine levels to rise and this is what acually 'shocks' the water. In either case you must wait for the levels to drop below 10 ppm before entering the spa so the main advantage to MPS in a chlorine system (only a short wait after shocking) is non existant in a bromine system because the chemistry involved is different.
With an indoor chlorine system MPS can be usedful in preventing the formation of combined chlorine and can help in maintaining better indoor air quality!
I've tested more water than I ever care to think about!
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#10 zoetman

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Posted 24 December 2007 - 10:20 AM

QUOTE(waterbear @ Dec 23 2007, 11:31 PM) <{POST_SNAPBACK}>
QUOTE(zoetman @ Dec 23 2007, 09:12 PM) <{POST_SNAPBACK}>
thanks Richard. I think I'll stick with the dry acid. I also had a question. You( or someone) mentions that you don't necessarily need MPS with a bromine system. What about with a chlorine system (dichlor). My spa is indoors. Thanks Beverly

Actually, it was me. In a bromine system MPS is generally used as an oxidizer but is wrongly referred to as a shock. Chlorine is just as effective and quite a bit less expensive for this purpose with bromine. MPS has no advantages in a bromine system since either MPS or chlorine will cause the bromine levels to rise and this is what acually 'shocks' the water. In either case you must wait for the levels to drop below 10 ppm before entering the spa so the main advantage to MPS in a chlorine system (only a short wait after shocking) is non existant in a bromine system because the chemistry involved is different.
With an indoor chlorine system MPS can be usedful in preventing the formation of combined chlorine and can help in maintaining better indoor air quality!



thanks waterbear!




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