Max amount of Muriatic Acid to add when balancing ALK and PH after refill?

duganderson

Well-known member
Jan 26, 2021
148
Minneapolis
@Nitro wrote up an AWESOME and clear description of lowering ALK and PH in 2009 (see below). Nitro said to use 1/2 the amount of acid necessary to reduce ALK to the target level (I use target of Alk = 50). He said to not use more than than 1 cup of acid at a time. I think, however, he was referring to dry acid.

What is the max amount of muriatic acid (Acid Magic 31.45%) in fluid oz. you can add at one time in this step (step 3 according to his directions below)?

Also, is this method quoted below still considered safe on equipment and efficient even though it was posted in 2009? (I realize the chemistry does not change but wondering if there is a different understanding of impact on equipment, etc.)


*****The rest of this post is quoted from the relevant section of Nitro's post which is located at Lowering Total Alkalinity

"1. Turn on all your jets and air features and keep them on the entire process. (i.e. Aerate)

2. Calculate how much you want to lower your TA, and how much acid you need to add to lower it.

3. Add to the tub HALF (not > 1 cup nor < 1 TBS) of the amount of the remaining acid you need to add.

4. Aerate for 30min, and check TA/pH.

5. If TA > Target and pH is > 7.8, goto step 2.

6. If TA > Target and pH is < 7.6, goto step 4 one time.

7. If TA > Target and you can't get pH > 7.8 via aeration, Target too low. Stop here.

8. If TA = Target and pH is > 7.8, Target too high. Lower Target TA and goto step 2."


Thank you, Doug
 

Texas Splash

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That article is from a different forum and varies slightly from how we advise. While those instructions focus more on the TA number with each dose, we focus on the pH because in some cases (your area for example) with an extremely high TA in the local water supplies, there's no way you can add enough acid in one dose to go from say 300 to 60. So what we do is wait until the pH is at about 8.0, then use enough acid (usually liquid) to lower the pH to 7.0. That will safely lower the pH and TA in stages. Once you lower the pH, aerate to increase the pH while leaving the TA a bit lower. Repeat this process until you achieve the desired TA goal. Acid (in stages) to lower the pH from 8.0 to 7.0 followed by aeration is how we recommend it.
 

Texas Splash

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Just curious........one cup of dry acid equals the effect of how much muriatic acid (Acid Magic 31.45%)?
I don't think you'd ever want to put one cup (8 ounces) of dry acid in a 400 gal tub. Much too much. But to give you a comparison:

Given a TA of 60, to lower the pH from 8.0 to 7.4:
Dry Acid - 1.5 ounces
Muriatic Acid - 1.1 ounces
 

jseyfert3

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My tap water is between 325-400 ppm of TA. As mentioned, adding half the acid required to drop that to 50 would take the pH so low it would almost certainly damage the heater.

It’s annoying but I always do as outlined. Aerate with both pumps on high and all air valves open. When it reaches 8+ use PoolMath to calculate acid addition to drop to 7. Add that, continue running pumps and aerating until it reaches 8+, repeat. Test TA before each acid addition since the amount of acid to add drops as the TA drops.

What’s your fill water TA?
 

duganderson

Well-known member
Jan 26, 2021
148
Minneapolis
I just realized the Pool Math app allows you to build in a ALK number so can add a lot more Muriatic Acid at a time to go from PH of 8.0 to 7.0 if the ALK is high. I was using Pool Calculator which does not build in the current ALK so Pool Calculator was only having me add 1.333 oz of Muriatic Acid at a time which takes WAY more additions than the amounts specified in pool math when the ALK is high.

I should have figured this out based on jseyfert3's comment to "Test TA before each acid addition since the amount of acid to add drops as the TA drops" but I was on vacation in Iceland so I'll blame my lack of connection on that.
 
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