Alkalinity?

[mphare]

On of the pH drop test kits I have has a chlorine neutralizer that should be added when the CL level is high.

Isn't one of the solutions in the Taylor2005 also a CL neutralizer? Maybe you just need to add more neutralizer before measuring pH.

[CarlD]

Just to clarify:
Aerating does NOT lower alkalinity (TA). It raises pH without raising TA--and nothing else can do that.

When you lower pH, you drag TA down with it. If you raise pH with soda ash or borax TA will rise--more with ash than borax. So you aerate to raise pH.

So the process is a racheting process. Lower pH and drag TA down with it. Raise pH with aeration. Repeat until TA is where you want it.

[waterbear]

Just to clarify:
Aerating does NOT lower alkalinity (TA). It raises pH without raising TA--and nothing else can do that.

When you lower pH, you drag TA down with it. If you raise pH with soda ash or borax TA will rise--more with ash than borax. So you aerate to raise pH.

So the process is a racheting process. Lower pH and drag TA down with it. Raise pH with aeration. Repeat until TA is where you want it.

Actually, the TA (carbonate hardness, kH) is not lowered until the CO2 is forces out of the water by airation. (Lowering the pH simply shifts the ratio of carbonic acid/bicarbonate in the buffer to the carbonic acid side.) This forcing out of the CO2 by airation reduces the total amount of the carbonic acid/bicarbonate buffer system in the water. As the CO2 is forced out of the water by airation the shift is to more bicarbonate ion hence the rise in pH and the decrease in TA. The 'accepted way' (that does not work effeciently) of pouring a 'shot' of acid into the pool with no water movement to lower TA is supposed to work in the assumption that the local area of low pH created will cause the CO2 to 'gas off' in that area since it will create a high concentration of carbonic acid (CO2 dissloved in the water) in that area.

[CarlD]

Actually, the TA (carbonate hardness, kH) is not lowered until the CO2 is forces out of the water by airation. (Lowering the pH simply shifts the ratio of carbonic acid/bicarbonate in the buffer to the carbonic acid side.) This forcing out of the CO2 by airation reduces the total amount of the carbonic acid/bicarbonate buffer system in the water. As the CO2 is forced out of the water by airation the shift is to more bicarbonate ion hence the rise in pH and the decrease in TA. The 'accepted way' (that does not work effeciently) of pouring a 'shot' of acid into the pool with no water movement to lower TA is supposed to work in the assumption that the local area of low pH created will cause the CO2 to 'gas off' in that area since it will create a high concentration of CO2 in that area.

Evan,
While in terms of the actual chemistry, you are correct (as far as my limited knowledge goes), functionally (ie from the owner's point of view), the aeration simply raises the pH without raising the TA at the same time.

The underlying mechanism is as you describe--the effect is as I describe.

So the user's testing will show TA to fall when pH falls, then with aeration the pH rises but the TA does not. For the "How do I do it?" owner, this is sufficient. Usually, these are the folks who need help.

For the "How does it work?" types, your explanation is more precise.

BTW, the shot of acid method is not advocated here, either. It's good for ruining vinyl liners, though...

[waterbear]

Carl, What you say is totally true. However, airation will have no appreciable effect unless the pH is brought low enough to cause the shift in ratio. I was only trying to clarify that. The 'shot of acid' method that just about everyone in the pool industy advocates will just lead to pH bouncing all over the place as you try to balance everything out. I wondered about it the first time I read it when I got my first hot tub and was learning how to care for it! It went against everything I had learned from my experience in keeping aquariums! When I first saw the PROPER way to do it on this forum I knew I found a home and advice I could trust!

[savdoc2]

Thanks for all the technical and not so technical advice. I didn't realize that the TA levels wouldn't drop until the pH started rising again. I am quite concerned about my pH levels now. I am afraid that they are too low. My biggest problem right now id that it is an 80 mile drive to Leslies. I will call the few local pool stores and what type of water testing they do, just to get back up testing. I know that my HTH kit is not the best, but so far it is the ONLY kit I have found locally. Home Depot doesn't have any pool stuff out yet and Lowes only has a 2 way kit and strips. Even the pool store that we got the pool from only sells strips.

If I have gotten my pH too low, should I just wait until the aeration slowly brings it up or should I add some borax to bring it up slightly (and the TA too)? How low is too low for pH?

[waterbear]

IF your chlorine levels are very hight the only way to get an accurate pH reading is with a properly calibrated pH meter. Most pool stores do not use them, however. My opinion (and anyone please feel free to correct me if you think it is in error!) would be to:
1) let the chorine level drop to under 10 ppm (mix your sample of pool water with an equal amount of distilled water...a shot glass is a good measure) and then test it and multiply the reading by 2. This way you can test up to 10 ppm Cl instead of 5 ppm)
2) Then retest your pH and if it is extremely low add borax IN SMALL INCRIMENTS to bring it up to 6.8
3) Then follow the procedure in this thread exactly to lower the TA
http://www.poolforum.com/pf2/showthread.php?t=191

I noticed that you stated that the ALk was "190 (a purple color down from 240+ on the 23rd)" , Is the TA test in your kit a titration (where you add drops until the color changes) or is it comparing a reagent against a color chart, or maybe a test strip?(TA tests on pool strips are usually shades of green while TH ...Total Hardness... are blue to purple!) If it is not a titration test I would not mess with it at all until the water was tested with a titration test. This didn't register with me the first time I read it but as I reread through the post it set off a warning bell in my brain.

[jenmenke]

Just to clarify:
If you raise pH with soda ash or borax TA will rise--more with ash than borax. So you aerate to raise pH.

CarlD said that borax WILL raise TA. Is it just a little? I'm battling high alkalinity in my fill water all the time (300++) so I'm paranoid about adding anything that will increase TA once I get it into range. But PH of 7.2 seems a little low. But if aeration stops increasing Ph at 7.2, then I have to use something else, right?
Jennie

[Watermom]

Borax will not raise your alk much at all. That is why it is much preferred over soda ash. If you want to try and continue aerating to see if the ph will come up on its own, that is fine. Then, if it doesn't, you can always add a little Borax. (And, actually having a ph of 7.2 doesn't hurt a thing. Just keep an eye on it that it doesn't drop too low.)

[CarlD]

Jennie,
I guess I wasn't clear. Total Alkalinity is linked to pH and generally moves with it. If your pH goes down, T/A goes down. If your pH goes up, T/A goes up no matter HOW you raise it.

Except: Aerating when pH is 7.2 or lower is the only way we can "break" that link and get pH to up without T/A going up as well.

We can also raise T/A without raising pH (much)--by adding baking soda.

So using Borax to raise pH causes the normal linked rise in T/A.

But if you use Soda Ash it's like adding BOTH Borax AND Baking Soda and it causes T/A to rise a lot more than Borax.

Still, as WaterMom says, you can usually use Borax without worry. However, if you are still in the process of lowering T/A, and pH is 7.2 or lower, you can use aerating to raise pH as our normal procedure.

CAVEAT: If your pH is below 6.9 you'll want to raise ASAP with Borax, especially in a vinyl pool.