Confused About How To Lower Total Alkalinity..Decrease..

by David

I have found so many conflicting details about lowering Total Alkalinity, that I don't know where to turn. Your website impresses me, and it seems like you know what you're talking about, so I'd like your advice.

My TA is in the 180 range (determined by test strip) after we recently replaced the liner and refilled the pool with tap water. I'm going to use muriatic acid to lower the TA, and from what I've learned, I should add it in the deep end with the pump off and the surface calm. Then I should let it set for at least 2 to 3 hours before circulating again.

My questions are: What should the volume of each dose be? (I've read everything from one pint to a quart.) Do I or don't I scrub the bottom and when? (If I do it right away, won't it cause the "acid column" to disperse faster and risk lower pH too much instead of TA?)

I just put in a new 27 Mil. vinyl liner -- I don't want to back out to my pool and discover a big faded/bleached spot at the bottom of the deep end where the acid did it's damage.

How long should I wait before I add another dose? If I need to get my TA down from about 180 to around 80-100, I know I'll need to be patient -- especially if I can only add a pint at a time. (According to your chart, it looks like I'm going to need to add about 2.5 gallons total of muriatic to take care of this, right?)

Thanks for your help!

Thanks for the compliment David. You did come to the right place to learn about your pool water chemistry. I would first advise you to get a Taylor Reagent FAS-DPD K-2006 test kit. It's the best one on the market. A little getting used to but it's worth the time.

Water Testing Kit

There are two ways to lower the total alkalinity. One is with the pool pump off and another is with the pump on, using muriatic acid. Now, acid lowers both the pH level and alkalinity, so you need to "tell" the pool which one to lower. Here's the difference:

First, and I don't like this terminology, but it is used, is the "slug" method. This is my preferred method where the acid is poured at one spot in the deep end with the pool pump off. Very gently sweep the bottom of the pool to break up any "hot spots". Allow this to sit for 2 - 3 hours, turn the pump motor on, allow for one complete turn-over, about 10 hours, then re-test the alkalinity.

The 2nd method is with the pump motor on. Pour the acid around the perimeter and have all of your water features on, i.e. slides, water falls, kids splashing around, air compressor with a hose in the pool etc... It lowers both the pH level and total alkalinity. The water movement causes "aeration" or "gassing-off" which burns off the CO2 (carbon dioxide) and raises the pH level, but not too much of the alkalinity.

The reason I prefer the first method is when I was taking care of pools in Arizona, I didn't have time to bring out an air compressor to help raise the pH back up again. If I turned on any water features I would have to go back and turn them off, which is very time prohibitive when you have a route of 50 pools and driving around 150 miles per day. The lack of time to make corrections is the the same issue I have at the Y pool. I need to make them quickly because we don't have any water features and the pool can't be shut down for 2 - 3 hours while an adjustment is made.

Also, why lower the pH when all you need lowered is the alkalinity? It can be done with this technique. I've done it hundreds of times and it works. This is the same technique I use to raise the alkalinity with sodium bicarb. I didn't see what size gallon pool you have, but the chart on this page is correct:

Swimming Pool Alkalinity

The Y pool is 80,000 gallons and I use 1 gallon of muriatic acid to decrease the total alkalinity by 10ppm. 40,000 gallons would be 1/2 gallon of acid. For every 10,000 gallons you would use 0.8 qts. to decrease the total alkalinity by 10ppm.

Acid is heavier than water so when you add the acid it will sink to the bottom. There won't be a "column" of acid per se. So can very gently brush the bottom where the acid was put in to break up any spots and disperse the acid along the bottom, but this is when the total alkalinity is being decreased, and not the pH level. You will need to be patient because after adding the acid you need to wait for one full turn-over of the water, normally about 10 hours. This is where pool owners get frustrated.

They need to realize that adjusting pool chemicals takes time because it must go through the entire filtration system and retested before another addition can be made. This way you'll get the most accurate readings.


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Oct 19, 2013
alk 180 ph way low 6.8-
by: Anonymous

If I agitate the water with a compressor how long do I have to wait before testing and adding additional acid. And how long should I have the water agitate, 30,000 gal pool?

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