Lowering Alk -- fountain or ripple

[JohnT]

Today, I added muriatic acid and plan to aerate. So, am I to expect, based on what you've explained here, that my PH will plummet? That didn't happen last time...
Jennie Menke

No, you should expect your pH to go up. If the TA is still too high, add acid to get the pH back down, and then aerate again.

[jenmenke]

Why should I expect PH to go up? I think I'm confusing myself. Let me ask this:

If I wasn't aerating and added muriatic acid to address my high alkalinity, should I expect my PH to go down THEN? Because, like Carl says, alk and ph sort of tag along together?

... but by aerating I will combat the tendency for the ph to drop because of the added acid?

sorry. just trying to get my arms around this so it makes sense and I can remember it.

[JohnT]

Why should I expect PH to go up? I think I'm confusing myself. Let me ask this:

If I wasn't aerating and added muriatic acid to address my high alkalinity, should I expect my PH to go down THEN? Because, like Carl says, alk and ph sort of tag along together?

... but by aerating I will combat the tendency for the ph to drop because of the added acid?

sorry. just trying to get my arms around this so it makes sense and I can remember it.

Normally, pH and alkalinity move together, so when you add acid, they both go down. (You'll have to look at Ben's stuff to get the exact details, but here's my recollection of how it works) At lower pH, aeration causes carbon dioxide gas to be given off by the water. This removal of carbon is what actually helps. The aeration process raises the pH, but since the carbon has been gassed off, your TA stays down.

[jenmenke]

Normally, pH and alkalinity move together, so when you add acid, they both go down. (You'll have to look at Ben's stuff to get the exact details, but here's my recollection of how it works) At lower pH, aeration causes carbon dioxide gas to be given off by the water. This removal of carbon is what actually helps. The aeration process raises the pH, but since the carbon has been gassed off, your TA stays down.

So how long would you expect it to take for six small fountains (think large drinking fountain action) to raise the alkalinity from 7.2 to 7.4 in a 40,000 gallon pool? Days? Weeks? I have no idea.

I've lowered the alk from 240 or so to 160 with 2 gallons of muriatic acid. the ph went down from 7.3 to maybe 7 or 7.1. I've had the fountains on all day for the last 3 days. Would you recommend more acid? We DO have a heater and we HAVE blown out a heat exchanger from bad scale. That was in 8 weeks or so of use the first season. The pool company paid for it that time because they were the ones that told me that if my water was clear and ph was in range, I was fine. I found this site shortly after that. I just don't want the same thing to happen again. I would guess I still need to add more acid?

(oh and by the way, the last question I asked about shelf life? That older acid was completely bad. So I answered my own question: Yes acid has a shelf life, or it completely degrades when exposed to heat and/or cold)

[sparks999999999]

So how long would you expect it to take for six small fountains (think large drinking fountain action) to raise the alkalinity from 7.2 to 7.4 in a 40,000 gallon pool? Days? Weeks? I have no idea.

Newb here <wish i knew about this site a couple weeks ago> anyway i am interested in the answer to this question as well - how long does it take? Hours, days, weeks - or do you simply keep checking until PH stops increasing?

Thanks.

[waterbear]

Newb here <wish i knew about this site a couple weeks ago> anyway i am interested in the answer to this question as well - how long does it take? Hours, days, weeks - or do you simply keep checking until PH stops increasing?

Thanks.

Read this thread for the proper way to do it
http://www.poolforum.com/pf2/showthread.php?t=191

[jenmenke]

oops. forgot to ask one more thing.

what is the shelf life of muriatic acid? the acid I added was a bottle I've had for a couple of years that sat in a pretty cold garage over the winter.

thanks

[waterbear]

Chemistry nerd alert. I am trying to simplify the explanation of a confusing topic so if you already understand the chemistry involved you might question my explanation somewhat, If you understand it then this really isn't for you.
Ok, let me see if I can explain this without confusing anyone. Alkalinity is referring to what is also called carbonate hardness (kH) and that is a term that most aquarists are familiar with. It has to do with the carbonic acid/bicarbonate buffer system in the water. (A buffer system is something that helps keep your pH from bouncing all over the place and at a certain pH level. It consists of a mild acid and it's corresponding alkaline ion.)

If you lower pH you will shift it to more carbonic acid (which is just carbon dioxide gas, CO2, dissolved in water, also known as club soda) and less bicarbonate ion but the alkalinity of the water has not lowered.

If you now airate the water you will drive off some of the carbon dioxide (like shaking a bottle of club soda so it loses it's fizz), shift the balance of carbonic acid/bicarbonate to more bicarbonate in the water which will cause the pH to rise, and as a result actaually have less carbonate hardness, or alkainity (total amount of the carbonic acid/bicarbonate buffer), in the water. You have now lowered your alkalinity.

The reason that borax will raise pH without appreciable effect on alkalinity is that it introduces a second buffer system that consists of boric acid and borates.

Both sodium bicarbonate (baking soda) and sodium carbonate (pH up) will raise it but sodium carbonate has a higher pH and will also raise pH faster and higher than sodium bicarbonate. If you only want to raise pH without affecting the carbonate hardness or alkalinity then using borax is a better choice since it will have much less effect (although it will have some) on the carbonic acid/bicarbonate buffer system we all know as total alkalinity.

Hope this helps to clear things up.

to rephrase:
lowering your pH does not automatically lower the alkalinity...it increases the ratio of carbonic acid (carbon dioxide gas dissoved in the water) to bicarbonate ions but the total carbonate hardness or alkalinity is unchanged.
allowing the carbon dioxide gas to "gas off" while the pH is low will casue the pH to rise (becuase of the increase of bicarbonate ions to carbonic acid) and will leave you with less carbonate hardness, or alkalinity, in your water.