Alkalinity?

[savdoc2]

I just don't get it.

How can I keep adding acid and still get no drop in pH or Alk? I put in the last 7 lbs of dry acid about 4 hours ago and there is no change in either reading. I did buy some muratic acid at Lowes this afternoon, so as soon as my husband gets home I will add some of it and let it work overnight.

[waterbear]

I think I see what the problem is. I just noticed your chlorine levels are well above 5 ppm (bright orange on OTO test!) . If they are very much above about 10 then when you test pH the phenol red indicator is being converted to chlophenol red which is an indicator for a lower pH range! (some indicators are better than others...i.e. have a chlorine neutralizer built in, but this will only work to a point and some conversion of phenol red to chlorphenol red will still occur at high chlorine levels) It is entirely possible that your pH is below 6.0 now if your chlorine levels are very high! the color that chlorphenol red prduces at a pH of about 5.4 is similar to the one that phenol red produces at about 7.2! I suggest that you get your chlorine done at a pool store that uses an FAS-DPD titraton test (or buy such a kit yourself) and find out just how high your clorine level is. If it is above about 10 ppm then you should treat you pH readings as suspect until it drops down.

you will not see a deacrease in alkalinity until the pH starts to climb above about 7.4 so it might take airating for a while, given the low pH.

IMHO, I would not add any more acid right now until the CL levels drop to normal ranges.

First thing is to wait for the CL levels to drop below about 8 ppm and then test the pH. Once you know where it is then you will have a better idea what to do next!

[savdoc2]

Thanks for that explanation. I have Ben's kit ordered, so I hope it comes soon.

I am really surprised that my CL levels have stayed so high. I did wonder about the high CL bleacing the indicators. I will see if a local dealer does a titration test tomorrow.

[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...

[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.)

[waterbear]

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.

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.