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Lowering Total Alkalinity (Without Lowering pH)

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Nitro:
This topic comes up quite a bit. I explain the process in my Maintenance Guide, but I thought I'd post a separate thread for easy reference. I won't get into detail why you would want to do this here. See my guide for more info. I will say this, the key is, you should NOT focus on adjusting pH directly. Instead, you should focus on adjusting TA to an ideal level, in order to keep your pH in line. If you're using Bleach TA should be 50-60ppm, if using Dichlor TA should be 80-100 ppm and if using Bromine TA should be 100-120 ppm.

The problem with lowering Total Alkalinity (TA) is that when you add acid to lower TA, pH also decreases. This limits the amount you can lower TA without pH becoming too low. However, there is something you can do to raise pH that leaves TA alone, Aeration. Aeration is the process of turning on all the jets and air features in your tub, in order to pump as much air into the water as possible. By adding Acid and Aerating you can lower TA, while keeping pH the same.

One thing to remember is, the amount that TA decreases is directly proportional to the amount of acid you add. That is, in a 350 gal tub, 8 oz of Dry Acid will lower TA by 100ppm. It is important to know (by calculating) how much Total Acid you need to add to your tub in order to get to your Target TA.

The other thing to remember is, the higher your TA, the less effect acid will have on your pH. If your TA is high, adding acid won't effect it much. This confuses some beginners (and experts alike), which causes them to give up on lowering their pH. Because of this, you need to add more Acid in the beginning, and less as you get closer to your Target TA.

So, let's get started. Here is the process.

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.

Example:
Your TA is 300ppm, you want to lower it to 60ppm, in a 350 gal tub.
To lower TA by 240 ppm you need to add a total of 2.4 cups (~19oz) dry acid.

Turn jets/air on.
Add 1 cup acid and Aerate 30mins.
Check TA/pH. TA=200 and pH>8.0
Add 6 oz acid and Aerate 30mins.
Check TA/pH. TA=125 and pH>8.0
Add 3 oz acid and Aerate 30mins.
Check TA/pH. TA=90 and pH>8.0
Add 2 oz acid and Aerate 30mins
Check TA/pH. TA=65 and pH=7.8
Add 1 TBS acid and Aerate 30mins
Check TA/pH. TA=60 and pH=7.6

The main thing to remember is, you add more acid in the beginning of the process, and taper off toward the end. This method will allow you to lower your TA in a matter of a few hours regardless of how high your TA is.

Lastly, safety is priority one. Be careful with any type of acid, especially Muriatic. If you're using Muriatic acid, wear rubber gloves and eye protection. Muriatic Acid is nasty stuff. Dilute all acid in a bucket of water and slowly pour mixure over a return flow, or middle of tub. Be careful not to splash. When mixing Acid and Water, always add Acid to water! NEVER ADD WATER TO ACID!!!

Happy Tubbing!  :)

Hillbilly Hot Tub:
Whats you take on raising ALK without raising PH....Say a 10 ALK with a PH of 7.8.
Curious to your suggestion on this, maybe I missed it somewhere.

Nitro:

--- Quote ---Whats you take on raising ALK without raising PH....Say a 10 ALK with a PH of 7.8.
Curious to your suggestion on this, maybe I missed it somewhere.
--- End quote ---
To raise TA just add Baking Soda. It will raise TA, but won't raise pH very much. i.e. In a 400 gal tub, 1 oz BS will raise TA by ~11 ppm, but will only raise pH by ~0.02.

Vinny:

--- Quote ---To raise TA just add Baking Soda. It will raise TA, but won't raise pH very much. i.e. In a 400 gal tub, 1 oz BS will raise TA by ~11 ppm, but will only raise pH by ~0.02.
--- End quote ---

Not true!

In my 400 gallon tub I use baking soda to raise both TA and PH. I can get my TA from 80 to 120 and PH from 7.2 to 7.8 using baking soda.

In my 13,000 gallon pool - it has no effect on PH. I use borax for raising PH.

Nitro:

--- Quote ---
Not true!

In my 400 gallon tub I use baking soda to raise both TA and PH. I can get my TA from 80 to 120 and PH from 7.2 to 7.8 using baking soda.

In my 13,000 gallon pool - it has no effect on PH. I use borax for raising PH.

--- End quote ---
Sorry Vinny, it is true. Chem Geek will confirm this.

The reason your pH rises in your hot tub and not your pool, is because Aeration causes pH to rise. When you add Baking Soda, only your TA rises. However, that ALLOWS pH to rise via aeration. The fact that it doesn't work the same in your pool confirms this fact. If there is little to no aeration, pH won't rise.

As I have said before, the only reason to raise TA, is if pH is too low and won't rise from aeration.

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