Alkalinity?

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Originally Posted by 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.

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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.

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Originally Posted by 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.

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chlorine neutralizer (sodium thiosulfate) will work to a point but if too much it used it will also have an effect on the pH reading.

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Originally Posted by waterbear

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.

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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...:mad:

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!:confused: 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!:)

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?

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.

The TA is a titration test. 25ml of pool water, add 5 drops of the reagent and then count drops of the titration agent until it turns from green to red.

I haven't gone out to get any water yet today - my daughters have been high maintenance this morning. I will go buy some distilled water later.

I think I am concerned about the pH from the explanation earlier about the high CL level changes the pH reagent.

Evan and I are on the same page here.

The WalMart HTH 5-way kit is really very good, but with super-high chlorine levels you may have problems with pH.

I had forgotten to mention that pH must be at or below 7.2 for aeration to work.

I've been an advocate of the shot-glass method for years. You can even use 2 shots of distilled water to one of pool water to measure chlorine levels to 15ppm with the 5-way kit.

Unfortunately, if you don't have the chlorine neutralizer, it's tougher to get an accurate reading--unless you have the Taylor phenol red that has the neutralizer in it.

Made it out to the pool. I got the following readings:

TC = 5+ I don't have any distilled water yet
pH = 6.8 or below since that is the lowest reading on the chart
TA = 140 - was a solid red

You have two choices:
1) add Borax NOW to get your pH to 7.0, then aerate to raise pH.
2) start aerating now and that will raise pH. But you'll need a fountain to raise pH quickly.