Hello group, I have a hot tub I am trying to balance the water. Both my Alkalinity and PH were high. I put in "PH down" and of course it lowers both. Is there a way to lower the alkalinity without making the PH bottom out?
Thanks so much! John
Am I missing something? pH is a measure of the relative acidity or alkalinity of a solution (actually the concentration of hydrogen ions). pH less than 7 is considered acid (the lower the number the more acid the solution). 7 is considered neutral. Greater than 7 all the way up to 14 is considered alkali (the higher the number the more alkali the solution).
Asking to lower the alkalinity without dropping the pH is like asking to drop the temperature without cooling anything off.
I don't own an operating hot tub but I did take chemistry many moons ago.
Many people are confused by this. Alkalinity is the property of the water that pertains to how well bases can neutralize acids. Alkalinity acts as a buffer of sorts. If Alkalinity in the tub is low, the PH will never remain stable. If you raise alkalinity too high, you will find it hard to either raise or lower PH.
PH and Alkalinity are closed tied together, but they are not the same thing.
CWM
John,
Do you have access to you hot tub dealer?
Every time I fill, I take in a sample. They test it for free and give me a printout telling exactly what to dose and how much, and the time intervals between doses.
And they don't try to sell me massive amounts of chemicals. Usually just takes a few TBS of Ph decreaser over a period of several hours.
No, I don't think you're missing anything except possibly the terminology of the "water industry". I'm a molecular biologist, and I consider myself to have a pretty good working knowledge of chemistry, and I work with acids and bases regularly. In my experience (multiple research and teaching labs, several chemistry classes), the terms "alkaline," "basic," and "high pH" are used interchangeably, so your temperature change analogy is correct.
However, after a few minutes of web searching, it appears that the "water industry" (apparently someone who works with hot tubs, aquaria, etc.) uses the term "alkalinity" the same way I would use the term "buffering capacity". Seems like they like to say, as another poster has pointed out, that alkalinity refers to how well a solution resists change in pH, or the amount of acid that must be added to change pH.
So in common use, I would say you're right: alkalinity is the opposite of acidity. But it seems like the OP has a hot tub that's basic (high pH), and too strongly buffered. When he added "pH Down" (i.e. an acid), the pH of course dropped, and he must have overcome whatever buffering capacity the water had, thereby reducing the "alkalinity". I know from experience in the lab that it's easy to overshoot your target pH when adding acids or bases, and that buffers can be tricky things to maintain when you try to drastically change the pH. So the advice of others to start over with new water, (effectively make a new buffer around your target pH), makes a lot of sense to me.
Sorry I'm not much more help on the hot tub side of this question, but the changes in terminology are interesting. As you can probably tell, I don't own a hot tub and I have very little experience with them, but I'd love to be sitting in one right now.
Good luck with your pH and alkalinity adjustments, Andy
I don't worry much about the alkalinity in the spa. Just get the PH where you want it, then the sanitizer as needed. I rarely use anything except di-chlor and baking soda once in a while.
Note that if you get the PH where you want it, and then add sanitizer, the PH will no longer be where you want it. Sanitizer will lower the PH, especially if you have not established proper alkalinity.
CWM
No. pH is the "potential of hydrogen ion," and is directly related to alkalinity and acidic. I suggest changing the pH more slowly, adding "PH Down" every other day and testing days in-between.
Lower the pH to 7.0 and _maintain_ it at that level while aerating the water. The aerating will speed up the outgassing of CO2. When the alkalinity is where you want it then stop correcting the pH and keep aerating until the pH is where you want it.
Not true. You always ph before sanitizing. you obviously don't have a pool or hot tub.
Please let the rest of us know when you get a clue. For openers, "PH" is not a verb.
CWM
Hi, Andy. Another molecular biologist here. I was scratching my head at first, too, wondering how he make his tub less alkaline without reducing the pH. Thanks for your post; I agree that the "tub industry" is using the term alkalinity imprecisely. I too would use the term buffer capacity. I wonder just what kind of buffer a hot tub uses. PBS? TAE? TBE? Tris-glycine? 20 mM HEPES?
Have a good day,
Bill
Bill & Andy-
Thanks for jumping in here on this spa water chemistry discussion.....
I, too, was thinking that the spa/pool people were using the term alkalinity imprecisely because it didn't make sense to me.
I figured they were trying to describe a buffered solution without getting into the chemistry of the situation.
Having had a spa for 10+ years (moved recently) ......I was lazy & never really put my chemist hat on but just followed the water conditioning treatment instruction by rote.
Most of the time it worked fine but occasionally the chem got all messed up & I would just drain the spa & start from scratch.
I think if the spa/pool industry gave people better information, it would easier to understand what is really going on & control it.
cheers Bob
(Mechanical engineer, I took a detour from my chemistry major 35 years ago) :)
This has been a good thread. I've often thought the use of the term alkalinity by hot tub companies was a little "off", but since I knew what they were trying to get me to do, it wasn't an issue. It did sometimes make me wonder if I was somehow mis-remembering what I learned in school. Tub and pool chemistry really isn't that hard to maintain once you have been doing it for awhile. The basic concepts are quite simple, and most mistakes are made by trying to hurry things up with too-large doses, or trying to adjust two different aspects at once. A Hot Tub's water is a little harder to maintain than a swimming pool simply because it's a much smaller volume of water, and that greatly amplifies anything you do. The difference between pouring a teacup of water into a bucket, and pouring a bucket of water into a teacup.
CWM
This site is interesting reading.
Carbonates/bicarbonates, expressed in ppm CaCO3. In outdoor pools there could be a second minor system, cyanuric acid/cyanuric anions, and possibly a third, borates/boric acid. We're interested in the carbonates/bicarbonates system and may apply a pH dependent "correction factor" if the cyanuric acid concentration is above a threshold. (The test measures total alkalinity, we just want the CaCO3 component).
Bill, Thanks for the reply - my first thought was 1X TE. Anyone need a hot tub full of DNA? You'd want to go easy adding the "pH down" to that tub, though... Andy
I still don't know why we are spending so much time on this. Even at the inflated cost of our water, with sewer charge added on, a hot tub will only hold a buck or two worth of water. Dump it
reading.http://askalanaquestion.com/spa_ph_and_total_alkalinity.htm>
There are products that will increase "total alkalinity", while not RAISING PH as much as a product designed to affect PH.
BTW, I agree with those saying that the alkalinity term as used in the water world is misleading. I also agree with whoever it was above that said they adjusted PH after adding sanitizer. I do routinely do this, because the sanitizer affects the PH. When I fill my SPA the incoming water is just about 7 to beging with, which is close enough to just add sanitizer.
Here in the Northeast, it costs a few more bucks for the electricity to heat that new, ice-cold, water up!
CWM
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