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Posted: 10/17/2016 9:12:00 PM EDT
I have 900 gallons of water, the water is soft, and has a pH of 7.0 and I need it to have a pH of 5.6.
I'm using phosphoric acid 75% food grade. The computer formula I'm using tells me to add 420 ml of acid,but
when I add and mix I get a pH of 4.3

After dumping a few hundred gallons and refilling it to 900 again I slowly added the acid,less than 30 ml at a time,mixing,
and then check the pH till it was right.

Does anyone know a formula to check the computer? I will be using the same acid and water, unless the city does
something. I could get more info if needed.

Thanks for any help.
Link Posted: 10/17/2016 9:24:28 PM EDT
[#1]
Use a smaller sample and test then use the proportion to the whole tank.
Link Posted: 10/18/2016 1:28:47 PM EDT
[#2]
Without also adding a buffer to stabilize the pH it is going to be very difficult.
Link Posted: 10/18/2016 2:23:19 PM EDT
[#3]
How close to 420ml were you when the target pH was reached?
Link Posted: 10/18/2016 9:15:31 PM EDT
[#4]
Discussion ForumsJump to Quoted PostQuote History
Quoted:
How close to 420ml were you when the target pH was reached?
View Quote


I started at 350ml because the last time we used the computer it was off so I used less
then it said to use. The pH went down to 4.6, I think. Dumped a few hundred gallons and started over
adding a little at a time till I reached to right pH.

Hoping someone knew of a formula I could use to check the computer.
Link Posted: 10/22/2016 4:41:26 PM EDT
[#5]
Quoted:
I have 900 gallons of water, the water is soft, and has a pH of 7.0 and I need it to have a pH of 5.6.
I'm using phosphoric acid 75% food grade. The computer formula I'm using tells me to add 420 ml of acid,but
when I add and mix I get a pH of 4.3

After dumping a few hundred gallons and refilling it to 900 again I slowly added the acid,less than 30 ml at a time,mixing,
and then check the pH till it was right.

Does anyone know a formula to check the computer? I will be using the same acid and water, unless the city does
something. I could get more info if needed.

Thanks for any help.
View Quote


Stop using the computer, and do the math. Really.
Link Posted: 10/23/2016 9:14:05 PM EDT
[#6]
Since you are using a triprotic acid, things are not straight forward.  There is no easy equation to get the answer.  

I saw this question last week and had to dig out my quant book from college.  Beause of the pH that you are trying to get to, more than one proton will be disassociated.

I tried to do a quick & rough calculation and I came up with about 130 mL of acid needed to get to the 5.6 pH.  I would need to do things a bit more exhaustively to get a better answer......









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Member, Friday the 13th
"Nothing tastes as good as skinny feels"  K. Moss
You can NEVER be too rich or too thin...
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Perfection: is not a goal---it's a demanded expectation.
Link Posted: 10/24/2016 12:44:47 AM EDT
[#7]
Link Posted: 10/27/2016 4:47:08 PM EDT
[#8]
Unless the water is VERY pure (like deionized) and carefully protected the typical remaining ions will alter the pH as soon as the temperature changes.

Do the math and investigate buffering.

Deionized water is a very poor conductor and used in discharge machining systems.

The operation of the discharge system puts enough junk in the water it needs to be filtered continuously.
Link Posted: 11/24/2016 10:43:23 AM EDT
[#9]
Never mind.  Just re read original post and what I wrote doesn't apply.  
-Kreate
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