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Using Muriatic Acid


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#1 countrygal

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Posted 13 November 2007 - 01:31 PM

I have been reading the posts here for several weeks and found alot of good information. I do have a question, I am trying to bring down the pH from around 8.0 to about 7.2. The Alk is at around 80. The spa is 300 gal. I am doing this by putting in Muriatic Acid since that is what I have. I have already added about 1 oz. with no change in pH over a 4 hour time frame. I am very concerned about this acid since it is so caustic. My question is how much should be added and over what period of time. When I get the balance to move down I will then rotate airation, Acid and baking soda to get the pH to 7.2-7.6 and alk. to around 50. I just don't know how to safely us this Muriatic Acid.

#2 chem geek

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Posted 13 November 2007 - 06:45 PM

To answer your question precisely, I'd need to know the Cyanuric Acid (CYA) level since that also acts as a pH buffer, though not as strongly as the carbonates which compose most of TA. At a CYA level of 50 and the other numbers you provided, it would take 3/4 fluid ounces of Muriatic Acid (31.45% Hydrochloric Acid) to lower the pH from 8.0 to 7.2. You might have a higher CYA which would take more acid (100 ppm CYA takes about 1 ounce for the same movement in pH) and your acid might be half-strength (look on the bottle for the percentage of hydrochloric acid).

When you add acid, you should have the circulation pumps running and should VERY slowly add the acid over a return jet so that it mixes thoroughly. For extra safety, I would take a bucket and fill it with spa water and add the acid to the water in the bucket first (you always add acid to water to prevent splashing -- never add water to concentrated acid), stirring it (not with your hand, obviously, but with a stirrer) and then slowly add the bucket of acidified water to the spa over a return jet.

If you have been running your jets during the 4 hours before you remeasured, then the pH will go back up from the outgassing of carbon dioxide.

The procedure to lower the TA is shown in this post. If you do get your TA lowered, then you should find less of a tendency for the pH to rise. By the way, what source of disinfectant are you using? Did you start out with Dichlor and are now using unscented bleach? Usually while one uses Dichlor and, to a lesser extent, MPS non-chlorine shock, the pH won't rise as quickly as these are both acidic (the Dichlor is acidic when accounting for the usage of chlorine which is an acidic process).

Dry acid (sodium bisulfate) is easier to use in a spa, but so long as you are careful in adding the Muriatic Acid, it is OK to use. I assume you are using a good test kit for your measurements such as the Taylor K-2006 or the tftestkits.com TF100 (these are test kits for chlorine, not bromine, though the TF100 has an OTO test that can be used for both).

By the way, you do NOT add baking soda to lower the TA to 50 -- Baking Soda raises the TA level. To lower the TA, you use a combination of aeration and acid addition done at low pH as described in the post I lined to above.

Richard

#3 countrygal

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Posted 13 November 2007 - 08:26 PM

Thanks for your response Richard. I don't know what my CYA level is since I don't have anything to test it with, I will be ordering the Taylor kit soon. I can tell you that I have only been putting MPS in the spa for the last several weeks as this is what I was told to use with the Sun Purity Mineral Sanitizer. I put a Tbs. in each day after I use it. I also have ozone. This morning I did shock with 6% clorax, waited for the chlorine to go down then put in the Acid, 1/4 oz. turned on the jets for 20 minuets with top off then closed the top waited 1 1/2 hours and tested. Still the pH was at 8.0 so I repeated and tested again an hour later and no change in pH. I did not want to add more Acid for fear that I was doing something wrong so I stopped and asked for help.

I am trying to follow the steps outlined in the post you referred me to, thats what started this whole operation. I understand that Baking Soda will increase the Alk. When I mentioned it above I was thinking that the Acid would lower the Alk. below the 50 mark by the time the pH got to where I wanted it to be.

Since adding more Acid will be OK, I will retest in the am and then add more Acid 1/4 oz. at a time until I get the pH down to 7.0 then Aerate until pH goes up to 7.2 then Acid back down to 7.0 and continue doing this until the TA is at 50. Is that about right?

#4 countrygal

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Posted 14 November 2007 - 12:09 PM

Wow, I must have a very high CYA level, it took a total of 3 oz. of Muriatic Acid to bring the pH down from 8.0 to 7.2 The Alk is now between 40-80 ppm. I am going to stop here and waite until I get the CYA tester to see exactly how high it is. I suspect I will have to drain and refill and start this all over again. I am confused as to why the CYA got so high, I have been only using the spa once per day or every other day for about 2 months. I have only been using MPS, 1 tbs. each time I go in and then once a week I put 3 tbs. in to "shock". When I refill I will use MPS for 2 weeks then switch to clorax, of course by then I will be able to monitor the CYA level and watch how it reacts. I should have been reading these posts 2 months ago!

#5 countrygal

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Posted 14 November 2007 - 01:26 PM

Test strips suck! I decided to take a water sample to the local pool company and had them test it. The results are much diff. then what I read from my test strips, the results are as follows:
pH 7.0
Alk 0
CYA 0
Calcium 0
Total Dissolved Solids 1000
Free Chlor 0

They suggest adding 3/4 cup Alkalinity increaser and 1 tbsp chlor. con. and then bring a sample in on friday to be re-tested. Can I use 3/4 cup of Baking Soda? and Should I use MPS to start to bring up the CYA and aeration to bring up pH? Any help would be most appreciated as my grandson is comming on Saturday and I know he will want to use the spa and I don't want to send him back with a rash.

#6 chem geek

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Posted 14 November 2007 - 03:17 PM

It's true that test strips are not very accurate except for a small subset of tests including salt, borates and possibly MPS. I'm not so sure I'd completely trust the pool store either. Having 0 Calcium Hardness is not realistic (even tap water has some hardness -- even if it's "soft" water) and having 0 Total Alkalinity is even less likely. Water that is exposed to air at a pH above 7.0 will still have some TA though it will be low (if the pH is really 7.0 and all the carbon dioxide has been driven out of the water, then the TA will be about 3 so < 10, but if the pH is higher then the TA should register as needing at least one drop of titrant). If I were you, I'd wait until you get your K-2006 before doing anything else except the following, mostly for safety. I would just add a small amount of baking soda -- about 3 or 4 ounces weight which is around 2-3 fluid ounces or about 1/4 to 1/3 of a cup. I think 3/4 cup is way more than is needed. When you add this to the water, notice if it looks like it is bubbling -- if it does, then the pH is very low and you should add some more baking soda; otherwise the pH either is OK or will be after the baking soda mixes in.

I'd be more concerned with the lack of disinfection over a long period of time since using only MPS non-chlorine shock is the wrong advice. You have to use some sort of sanitizer to kill bacteria. MPS alone will not do that. So assuming your chlorine test is decent, add some Dichlor to the spa assuming you've never added any since your last refill so that your CYA level is truly zero. The Dichlor will add both chlorine and CYA to the water. I would just add one ounce weight of Dichlor which is roughly one fluid ounce (2 tablespoons or 6 teaspoons). Each subsequent day, add 3 fluid ounces (6 tablespoons) of unscented bleach (don't add Dichlor again until after your next drain/refill of the tub).

The tub should be safe by the weekend if you use chlorine every day as prescribed. Who knows what the real pH is, but even if it's 8.0 that's not a terrible problem. The pH most likely will not climb that much above 8.2 to 8.4 anyway -- though it would be better to get the pH lower, I don't trust your pH test strips.

Once you get your Taylor K-2006, you'll know what's really going on and can then report back here and we can get your tub in good shape. I suspect you'll just need a minor pH adjustment.

Richard

#7 countrygal

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Posted 14 November 2007 - 04:20 PM

Thanks Richard, I was also surprised by the low readings but with all the acid I put in I figured something was wrong. I was not surprised by the 0 calcium, I am on well water and I always have to add calcium to my above ground pool (21'X41') each spring. 3 years ago, when I first got the spa the pool co. had me add calcium to the spa but the last two years they have said not to bother adding calcium even though the readings were always 0. BTW today when I took the sample to be tested I asked them to make sure they tested for CYA they said they usually do not test for that on a spa and didn't seem to understand my concern for the level getting to high. Anyway, thanks again for your advise and I will follow it and await my Taylor K-2006 kit.

#8 chem geek

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Posted 14 November 2007 - 06:27 PM

If you used Dichlor as your source of chlorine (it sounded like you were only using MPS and not chlorine, however), then you would build up CYA. Apparently they do not understand that Dichlor adds both chlorine and CYA.

#9 countrygal

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Posted 14 November 2007 - 08:20 PM

QUOTE(chem geek @ Nov 14 2007, 06:27 PM) <{POST_SNAPBACK}>
Apparently they do not understand that Dichlor adds both chlorine and CYA.


I wonder how many spas in my area have very high levels of CYA with out knowing it, since this pool company is only one of two in town. They gave me a brochure from Spa Essentials that said to keep my Alk. up to between 125-150 ppm. I have instructions from SunPurity Mineral Sanitizer that says to keep the Alk. to between 80-120 ppm. It can all get rather confussing. But It makes more sense to me to keep it down to around 50 if that helps stop the pH fluctuation. Do you still feel that I do not need to increase the calcium?

#10 chem geek

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Posted 14 November 2007 - 08:42 PM

A low TA only makes sense if your spa has a tendency of the pH to rise as most do because of the aeration from the jets. But if the pH tends to go down due to the acidity of Dichlor and MPS, then you would want more TA. So there's no single answer -- it depends on the specific situation. I'd wait until you get a good test kit before deciding on such things.

It's possible for the well water to have low CH, but it would be unusual. Again, I'd wait until you get your own accurate test kit before doing anything other than what I prescribed (chlorine and baking soda). It's rather easy to increase CH, but decreasing it can only be done with a partial drain/refill (assuming the fill water is low in CH).

It's really disturbing how your pH test is 8.0 and theirs is 7.0. The pH test, even with test strips, is pretty hard to get that far off.

Anyway, sit tight until you get your own test kit. Just do the chlorine regimen I described and add a little baking soda and your spa should be OK to use.

Richard

#11 countrygal

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Posted 15 November 2007 - 07:53 AM

Richard, you really have a good way of explaining things. I need to make one clarification, after adding the acid my test strip read pH 7.2 with TA between 40 and 80ppm. The pool company results were 7.0 pH and 0 TA, so the pH was not that far off but the TA was, on my strip a 0 ppm is very clear. Anyway, I am following you directions and will get back with results. Thanks again for all your help




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