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I am stuck with PH and Total Alkalinity opposite each other.

Can someone help me make sure my though process is correct.

1) Add Sodium Carbonate to raise PH to about 7.8 (I believe I can add about 2lbs per day as my pool is 25,000 gallons).

2) Once PH is about 7.8 add Muriatic acid in columns with pump off to lower alkalinity and have limited effect on the ph (but enough possibly bring it down to 7.2 or so?)

3) Once alkalinity is about 120, raise ph to 7.5?

basically my thought process is bring the ph up a little high, lower it while lowering alkalinity, raise the ph, lower it and the alkalinity again...

I've been down that road before... you can use caustic soda (aka Sodium Hydroxide NaOH) to raise the pH without affecting TA. The best source I've found is Red Devil Lye where you find cleaning supplies. Be careful with this stuff, it's really nasty -- wear gloves and eye protection.

By the way I'm no expert but I'm dubious of the "pour in columns" thing. It never made any difference for me, and besides, an ion is an ion right?

Good luck,

Mike

On 5/16/2006 11:43:09 AM, Mike Stangel wrote:
>
>By the way I'm no expert but
>I'm dubious of the "pour in
>columns" thing. It never made
>any difference for me, and
>besides, an ion is an ion
>right?

I think someone had unexpected results due to some unknown parameter being different, wrote an aticle about it and the kool aid drinkers made it a fact.

I agree, it does nothing.

The way in which you add acid will effect either the pH or TA (more than the other). I have done the 'pour in column' method many times, with definite success. Always fix the TA before adjusting pH.

Do you know of a scientific reason for this?

Let me follow up to my own question, because I'm not trying to be a jerk here. Buffering is a concept that still escapes me no matter how much reading I do; I don't understand how carbonates or bicarbonates can insulate pH from rapid changes, without simply raising the pH by themselves. I think if I understood the chemistry better, I might have an easier time keeping my own pH stable.

It beats me too Mike. Wish Bob Lowry was back on board and he'd answer it in a heartbeat. We probably couldn't understand his answer though!

In a 230k gallon pool I added 5 gallons of muriatic (poured in one location) into the deep end in the evening. left filters off till morning. Repeated the process on the third evening (I found it better to miss a day) with 4 gallons of acid. TA dropped from 175 to 120 while the pH bottomed out at 7.2 during the process. pH has now been stable for months at 7.6.

I have had similar success in smaller pools, 10k - 20k using as little as 1/4 - 1/3 gallon of acid. I know the column method works, but still not sure why.

Actually Bob has addressed this very question. In the topic "High Total Alkalinity and Low PH" [http://www.waternetonline.com:8080/read?30204,6] he wrote:

"Here is what I would do. You can add a max of 21 fl. oz. of muriatic acid per 10,000 gallons twice a day. That would be 74 fl. oz. or about 2 qts. + 10 fl. oz. each 12 hours. Leave the pump on and dilute each quart of acid in about 2 gallons of water. It does not matter how you add the acid but you want to keep it away from the vinyl and any metal and the pump suction. Don't worry, with a TA at 340 ppm, all of the acid you are adding will go toward neutralizing the TA and not lower the pH. (Well, it will as you add it but it will equilibrate.) "

...but perhaps his answer was specific to the fact that the poster's TA was so high to begin with.

Mike

I had to google cache it because onbalance is down.
Bob was in the footnotes of the article, I don't know the extent of his involvement. http://72.14.209.104/search?q=cache:AAlaORDMI7kJ:www.poolhelp.com/acidcolumn.html+acid+column+myth&hl=en&gl=us&ct=clnk&cd=1

Happy reading

Perhaps by understanding what is actually going on in the water might help.  Total Alkalinity is the measurable carbonates and bicarbonates in the water that are part of the buffering system. (For simplicity I am going to ignore cyanurates from stabilizer and borates from sodium tetraborate 'water enhancers' that might be present also).  The other part of this buffer is carbonic acid (essentially carbon dioxide dissolved in water--same a seltzer). When you lower pH you lower TA because you convert some of the measurable carbonate and bicarbonate into carbonic acid.  It doesn't matter HOW you add the acid, just that you add it and lower the pH. Now the trick is to get the pH back up without causing the TA to rise also. If you add a chemical that is alkaline you will raise pH but also convert some of the carbonic acid back into carbonate and bicarbonate and therefore your TA will rise also. Soda ash (sodium carbonate) will add a lot of carbonate to the water and will actually cause the TA to rise faster than adding sodium bicarbonate and it is possible to end up with a higher TA than initially.  If you add sodium hydroxide (lye) or sodium tetraborate (borax) then you will cause less of a rise in TA as the pH rises compared to soda ash.

The problem becomes how to remove the excess carbonic acid and cause the pH to rise and the answer is simple. Aerate the water.  This will cause the carbon dioxide to outgas and the pH will rise. (Just like shaking a bottle of seltzer to make it go flat.) Aeration is easy to accomplish by using a fountain or other water feature, turning the eyeballs up to break the water surface, or using an air compressor to cause air to bubble up through the water (much like an airpump and airstone are used in an aquarium). Even a rig made from PVC with a 90 deg elbow that causes the water to shoot into the air and then return to the pool placed in a return can be very effective.

The biggest problem with the process is that it takes time to gas off the carbon dioxide, depending on how vigorous the aeration is. The 'slug method' does not work and only creates pockets of very low pH that can damage pool surfaces. To effectively lower TA quickly and keep it down drop the pH to 7.0 and test TA, begin aeration and monitor pH. When pH starts to climb add more acid to drop pH back to 7.0 and test TA. Repeat until TA is at target value and stop adding acid and just aerate until pH rises to target value.