PH and Total Alkalinity - Are they the same?

Algae problems in swimming pool water. Green (cloudy) water or slimy pool walls. Black algae. Mustard algae. Pink or white pool mold.

PH and Total Alkalinity - Are they the same?

Postby Dave S » Mon 18 Sep, 2006 18:19

PH and Total Alkalinity - Are they the same?

What I mean is the following:-

Is Alkalinity a measure of PH?
A low Ph 7.0 means the alkalinity is low? and you
need to raise it with some Bi Carb?

They aren't two different things are they?

Why would the pool shop ask me to add Bi Carb one day and then put the Hydro-chloric acid the next day? wouldn't both chemicals balance each other out. (Acid/Akali)

I am getting confused?
Can you help?
Dave S
 

Re: PH and Total Alkalinity - Are they the same?

Postby me » Mon 18 Sep, 2006 19:46

Dave S wrote:PH and Total Alkalinity - Are they the same?

What I mean is the following:-

Is Alkalinity a measure of PH?
A low Ph 7.0 means the alkalinity is low? and you
need to raise it with some Bi Carb?

They aren't two different things are they?

Why would the pool shop ask me to add Bi Carb one day and then put the Hydro-chloric acid the next day? wouldn't both chemicals balance each other out. (Acid/Akali)

I am getting confused?
Can you help?

pH is the measure of how basic or acidic the water is. It affects sanitizer effectiveness and bather comfort. At a lower pH chlorine is more effective, it has more 'disinfecting power'. At a higher pH you may get clowdy water, scaling and deposits as the calcium in the water precipitates. Aim for a pH between 7.2 and 7.8.

Alkalinity (or carbonate alkalinity specifically for pool water) is a measure of the carbonates/bicarbonates in the water. These bicarbonate ions act as a buffer to minimize the swings in pH: It can be very difficult to adjust the pH if the alkalinity is too high, similarly, the pH can fluctuate wildly if alkalinity is too low. Aim for 80 to 120 ppm alkalinity.

A low pH may not indicate low alkalinity. They're two different things. You can have any combination of high/low pH with high/low alkalinity and each scenario has its 'side-effects'. For example a low pH with higher alkalinity, say 300, would make the pH drift upwards slowly to about 8.4, then you would get clowdy water and scaling. So people with high alkalinity have to constantly fight a rising pH until they get their alkalinity in check.

You raise pH with sodium carbonate aka soda ash and you lower pH with muriatic/hydrochloric acid or sodium bisulfate. Alkalinity you raise with sodium bicarbonate aka baking soda (same thing as in your kitchen) and you lower with muriatic acid (and time and effort).

You added the baking soda on day 1 to increase the total alkalinity, but baking soda also raises the pH a bit. Once the baking soda got circulated through the system and your alkalinity was corrected you added the hydrochloric acid on day 2 to lower the pH back to normal.

At the end of the day you should have both your alkalinity and pH within range and the pH should not fluctuate much, insuring clear water, bather comfort and sanitizer efficiency. You can check your pH regularly, say every two days and your alkalinity weekly. But don't micro-manage your pool, don't immediately try to correct a pH drop of 0.1 or 0.2 or an alkalinity drop of 5-10 ppm. A good investment will always be towards a quality test kit, the Taylor K-2005 comes to mind.

Best regards,
me
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Postby ccrb » Sat 31 Mar, 2007 20:01

I just opened my pool this weekend, and total alk was down, by about 50 lbs of bicarb. The pool supply store did the analysis for free, but the printout only lists brand names. Their cost for the powder was about 1.70. Walmart wasn't much better, but at least they listed the ingredient as bicarb. A trip over to the grocery area got me 2-lb boxes of Arm & Hammer bicarb for $1 each, or .50 per lb, less than one third the cost at the pool depts.

I appreciate the free analysis, but I'm hard pressed to pay three times the price because it has a picture of a diving board on the container.
ccrb
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Postby me_too » Wed 04 Apr, 2007 11:58

ccrb wrote:I just opened my pool this weekend, and total alk was down, by about 50 lbs of bicarb. The pool supply store did the analysis for free, but the printout only lists brand names. Their cost for the powder was about 1.70. Walmart wasn't much better, but at least they listed the ingredient as bicarb. A trip over to the grocery area got me 2-lb boxes of Arm & Hammer bicarb for $1 each, or .50 per lb, less than one third the cost at the pool depts.

I appreciate the free analysis, but I'm hard pressed to pay three times the price because it has a picture of a diving board on the container.


Right on. The cheaper stuff at the grocery store is the same thing as the product sold in the pool store, same active ingredient. It may be ground a little finer but it's the same ingredient. So go ahead and use it. Don't dump it all in at the same time, add about a half, retest the water, and add what's missing.
me_too
 

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