Alkalinity FAQ

I thought I'd repost the Alkalinity FAQ that PoolDoc had posted in this area of the old Forum, since I happen to have it saved:

#1109, "Alkalinity FAQ"



Alkalinity FAQ


What terms are used for "alkalinity"?
"Alkalinty", "Total alkalinity" (TA), "Carbonate alkalinity" (CA), etc.
There is a difference between CA and TA, but it's rarely important.


What should my TA be?
Somewhere between 50 and 200 ppm. If you've got a heater, it usually should be lower than 150 ppm. If you've got a plaster or concrete based pool, it usually should be higher than 80 ppm.


Why does TA matter?
TA is actually just a measure of how resistant to change your pH levels are, over a particular range. Sometimes, if your TA is too low, your pH will tend to change a lot, and be hard to control. Also, if you high TA is related to scale buildup inside your heater, or at your pool's waterline.


Why does CA matter?
CA is the portion of the TA that is due to "carbonates" from sodium bicarbonate (baking soda), sodium carbonate (soda ash), and other sources. On pools with concrete or limestone surfaces, low CA together with low pH will let your pool water DISSOLVE your pool surfaces, which is usually NOT a good thing. If your CA is high, your pool will tend to cloud up, any time you add calcium hypochlorite or raise the pH.


I still don't understand: what is alkalinity? Isn't the same thing as pH?
No, it's not the same as pH, but don't feel bad about being confused: most pool dealers, and many pool chemical manufacturer's don't understand alkalinity, either. Again, alkalinity is a not a 'thing', but a measurement. It's a measurement of how hard it is to change your pH. Exactly how pH and alkalinity are related has been discussed on the PoolForum, but is too complex to get into here.


Why does my dealer (or the NSPI, or my builder , etc) say my TA / CA must be just exactly such and such?
Historically, the concern for getting Alkalinity levels just so resulted from an attempt to use specialized mathmetical formula, developed for aiding boiler operators, on swimming pools. Later on, some of the chemical companies realized that the more exactly pool owners tried to control things, the more chemicals they'd sell. I suspect that this latter fact has a lot to do the pool chemical companies interest in 'just-so' chemical levels today.


Well, my TA is XX ppm; what should I do?
Usually, nothing! If you have a vinyl or fiberglass pool, no heater, no scaling, and no problem with your pH level changin erratically . . . don't worry about it!


OK, but how to I raise TA / CA?
Add baking soda, at the rate of about 2 lbs (or 2 cups) per 10,000 gallons of pool water . . . then retest.


But, I need to raise my TA 40 ppm, what's the right dose for that?
Add baking soda, at the rate of about 2 lbs . . .
Seriously, don't make the mistake dealers encourage of trying to get there all at once. Add some, and recheck. There are all sorts of reasons why this is the best way.


My dealer told me that I need the Alkalinity Increaser he sells, instead of baking soda. Why would he say that?
There are two reason. Either he's a liar or he's an ignoramus. Take your pick.


But is baking soda really the same? The dealer stuff has a chemical name of "sodium hydrogen carbonate". Is that the same?
Yes, it's EXACTLY the same. Baking soda is the pharmaceutical grade (extra pure) of sodium bicarbonate or sodium hydrogen carbonate. The pool store stuff is the industrial grade which is slightly less pure and is not as fine. But, except for impurities, they are identical.


Everytime I add baking soda, my pH goes up. How can I raise alkalinity without affecting my pH?
Usually, you can't. That's one reason (among many) for the 'add a little, and then retest' approach.


My TA is way too high. How can I lower it?
You can reduce your CA (the portion of the TA cause by carbonates) by lowering the pH and then aerating. The procedure is most be followed carefully, and is posted separately.


My dealer / builder / whoever said that the right way to lower TA is to add XX amount of acid. Should I do that?
No. The procedure for lowering TA (actually, CA) found in about 99.9% of the pool literature of the world does NOT work! What it does do is take you on an endless coaster ride up and down the pH and alkalinity scales. And, of course, you have to buy a ticket from your dealer each time you ride! As far as I know, it is STILL true that the ONLY place where a working process has been published is here.



Ben
PoolDoc




?
A

http://poolsolutions.com/ / http://poolforum.com/

Do you also have the info regarding using aeration to reduce alkalinity?

I know I have that aeration info someplace because I've used it myself a few times, but I can't find it as a file on either of my computers. I must have it printed someplace. When I find it I'll try to get it here, unless someone else reposts it in the meanwhile. It's the only way I've found to reduce the TA when the pH isn't also too high.

I reduce the pH of the pool water to below 7.2, usually around 6.9 - 7.0 or so. I point my return jets upwards to vigorously aerate the water surface.
The total alkalinity slowly goes down, but at the same time the pH also rises.
Once the pH reaches around 7.2 or so it needs to be lowered again to keep the process going until you've reached the desired TA. Once the alkalinity has reached a good amount I still aerate a little more to see how high the pH will adjust to on it's own, and once it's not going up from this process alone I add a pH increaser. (Borax will not affect the TA as much but I've also used plain old pH+, but it will bring the TA up with it somewhat.)

This process usually takes my 18x36 inground pool about 2 days of running this way 24/7 get get bring the TA down from around 135 to 100, which is where I like it for the chemicals I use.

Hope this helps.

Vickie

I didn't notice that PoolDoc posted the aeration procedure already under the title How To: Lowering Your Alkalinity.

Actually, I think I posted it after you'd already begun looking for it.

Thanks for posting the FAQ!

If you don't mind, I'm planning to update it a bit, repost it as a FAQ, and then delete this thread. But, it may be awhile, what with orders, getting the kit ready, and trying to get the @#@# server to stay up!

Ben