Pool store advice to lower alkalinity - three day muriatic acid dose method

[aquarium]

15,000 gallon IG plaster

Alkalinity here is naturally high out of the tap, pool tested at 220ppm. Their test said pH was 8.2, all mine say it's closer to 7.6.

Their advice: 1/6 cup muriatic acid in the water for one hour without the pump running then run pump for 23 hours, repeat, repeat. (Three days total)

Hardness is also naturally high, but a disproportionate amount is magnesium, almost a 2:1 ratio of calcium:magnesium when most waters are 3:1 or 4:1.

I don't see any scaling problems, so I'm not particularly worried about the alkalinity, but I am curious about the suggested method - anyone hear of this one?

[waterbear]

it's the 'accepted' method and it doesn't work very well. the idea is to pour a shot of acid in the still pool and the pocket of low pH will cause the carbon dioxide to bubble off....sort of like pouring vinigar on baking soda (which is pretty close to what your are doing!) I have read some descriptions of it where they say you can see the bubbling occur! You need to lower the pH and then aerate if you want to do it so it works!
See this thread
http://www.poolforum.com/pf2/showthread.php?t=191

[CarlD]

good way to remove the paint from the plaster.

Or melt a vinyl liner.

It's called the "slug" method and the ONLY way it works is if it inavertently brings you to the conditions that the aeration method uses.

[waterbear]

It's called the "slug" method and the ONLY way it works is if it inavertently brings you to the conditions that the aeration method uses.

I thought it was called the "slug" method because the guy who thought it up had the mentality of one!
(me bad!)

[aquarium]

Heh,

I'll live with it. I did turn the jets up so they break the water surface and cause some turbulence, but mostly for the 'water effect'.

[denanbob]

I received the same advice from our pool store. They said to add a cup of muriatic acid right near the return (I guess that is the closest to jet stream that I'll get). I guess I don't understand the difference between this method and the sticky post method. Is the difference just the aeration?

[CarlD]

Our method is precise, not a guess about what seems to work. If the guy who came up with the slug method was wearing a tin-foil hat they'd tell you to wear one of those!

The PoolForum method is
1) You lower pH to 7.0-7.2--since alk and pH are closely linked and move together, this pulls the alk down some.
2) now you aerate to raise pH without raising alk as well--there are reasons why aeration raises pH but doesn't raise alk, but the chemists here can explain it in the china shop. Raising pH with Borax or Soda Ash will raise alk back--soda ash makes it even higher.
3) Lower pH again to 7.0-7.2, again pulling alk down
4) Aerate again to raise pH without raising alk.
5) keep repeating as you ratchet alk down.
6) When you hit your target, aerate to get your pH up and treat your pH normally.

There's no hit or miss, this is how you do it.

[KurtV]

Carl, My guess is that your method will work just fine but it's a bit different than Ben's (which Waterbear linked to).

Specifically, you advocate allowing the pH to rise as you aerate while Ben calls for keeping the pH low while you aerate (with frequent testing and adding acid as needed).

As I said, I think that both methods will work but won't it take considerably longer if you let the pH rise repeatedly?

[CarlD]

Actually, Ben's method and mine are the SAME. We have refined his wording and the steps a bit to clarify it. We have clarified EXACTLY how Ben's procedure works.

Ben is still the source of this method, which DOES work for clear, definable reasons. It was ALWAYS a racheting-down procedure that performed repeatedly. All that has been is the "why".

[KurtV]

carl, From your post above: "...The PoolForum method is
1) You lower pH to 7.0-7.2--since alk and pH are closely linked and move together, this pulls the alk down some.
2) now you aerate to raise pH without raising alk as well--there are reasons why aeration raises pH but doesn't raise alk, but the chemists here can explain it in the china shop. Raising pH with Borax or Soda Ash will raise alk back--soda ash makes it even higher.
3) Lower pH again to 7.0-7.2, again pulling alk down
4) Aerate again to raise pH without raising alk.
5) keep repeating as you ratchet alk down.
6) When you hit your target, aerate to get your pH up and treat your pH normally."

From Ben's post on this (http://www.poolforum.com/pf2/showthread.php?t=191): "

1. "Test your ALK, and record it.
2. Decide what your target ALK is.
   If your ALK is high, due to some past dosing error, target 120 ppm, unless you have some reason to go lower or higher. If you anticipate a continuing problem with high ALK, say due to high alkalinity fill water, target 100 ppm. (These are not magic numbers -- if you have a reason, and understand your options, other values can work as well or better!)
3. Use small doses of acid
   to lower your pH to just above the lowest value on your testkit -- or 6.6, whichever is higher. Do NOT lower the pH to whatever the lowest value on your kit is! In many cases, if you try to do so, you'll ACTUALLY end up with a much lower pH, which can damage your pool. Instead, make SURE that your pH is at least a little higher than the lowest pH value your kit shows. Also, do NOT try to lower your pH all at once; for all sorts of reasons, it's important to do it gradually!
4. Begin aerating.
5. Test your pH AND your alkalinity.
   Continue adding acid to MAINTAIN your low pH until your alkalinity reaches your target value. Once it does, CONTINUE aerating, but allow the pH to rise to the normal level. (If it doesn't rise on it's own after several days, you can add small amounts of borax -- NOT baking soda or soda ash -- to bring it up.)
6. Once both pH and alkalinity are at target levels, stop aerating."

The bold/italics emphasis in both quotes is mine.

I'm not trying to nitpick or start an argument, but those two methods are fundementally different in a practical way. In the first, you allow the pH to rise as you aerate while in the second you actively keep the pH down.