Swimming Pool Blog


Swimming Pool pH and Total Alkalinity ~ Kissing Cousins!


by John Galcius, April 14, 2009
 

Total Alkalinity And pH In Swimming Pools
pH logoTotal Alkalinity and pH ~ close cousins I always say. Kissing Cousins. They are both measures of the relative acidity or basicity of your pool water. Keeping these cousins in line is important for bather skin and eye comfort, as well as for the care of your pool surfaces. Good levels also help keep your chlorine working most effectively. At higher levels, chlorine becomes very sluggish.
Total alkalinity or TA is a measure of the alkaline level in any body of water. In pool or spa water, the level of alkalinity is VERY important in your swimming and bathing comfort. Your TA should be between 125 to 170 for vinyl or painted pools and 80 PPM and 120 PPM for plaster or concrete pools. If you have a painted pool, and the paint is chalking, (rubbing off on your hands and feet), then the alkalinity is too low, and should be raised to at least 150 PPM. Another indicator of low Total Alkalinity is having a difficult time keeping your pH level stable.
When pH levels fluctuate widely over a short time period, take a look at your pool alkalinity level. When the total alkalinity is within this range, "stabilizes" the pH level and stops rapid pH changes.
 
Charts For Adjusting Total Alkalinity
Raising Total alkalinity In Swimming Pools Using Sodium Bicarbonate
GALLONS IN POOL
(PPM)
1,000
5,000
10,000
15,000
20,000
25,000
50,000
10
0.14 lbs
0.7 lbs.
1.4 lbs.
2.1 lbs.
2.8 lbs.
3.5 lbs.
7 lbs.
20
0.28 lbs.
1.4 lbs.
2.8 lbs.
4.2 lbs.
5.6 lbs.
7.0 lbs.
14 lbs.
30
0.42 lbs.
2.1 lbs.
4.2 lbs.
6.3 lbs.
8.4 lbs.
10.5 lbs.
21 lbs.
40
0.56 lbs.
2.8 lbs.
5.6 lbs.
8.4 lbs.
11.2 lbs.
14.0 lbs.
28 lbs.
50
0.70 lbs.
3.5 lbs.
7 lbs.
10.5 lbs
14.0 lbs.
17.5 lbs.
35 lbs.
            
Lowering Total Alkalinity In Swimming Pools Using Muriatic Acid
Decrease
GALLONS IN POOL
(PPM)
1,000
5,000
10,000
15,000
20,000
25,000
50,000
10
2.56 oz.
0.8 pts.
0.8 qts.
1.2 qts.
1.6 qts.
2.0 qts.
1 gal.
20
5.12 oz.
1.60 pts.
1.6 qts.
2.4 qts.
3.2 qts.
1.0 gal.
2 gal.
30
7.68 oz.
1.2 qts.
2.4 qts.
3.6 qts.
1.2 gal.
1.5 gal.
3 gal.
40
10.24 oz.
1.6 qts.
3.2 qts.
1.2 gal.
1.6 gal.
2.0 gal.
4 gal.
50
12.80 oz.
2.0 qts.
1.0 gal.
1.5 gal.
2.0 gal.
2.5 gal.
5 gal.
If the TA is too low, Pebble Tech and plaster walls will become pitted, metals will corrode, the pool's surface can stain, the water can turn green, eyes burn and we can have pH bounce (pH rapidly going up and down, seemingly at random). If the TA is too high, the pH is difficult to adjust, the water becomes cloudy, the pool constantly needs acid (according to your test kit) and the chlorine loses its efficiency as a disinfectant.
It is recommended that you test the TA regularly, but after initial adjusting, it will not change much in a well-maintained pool. To raise the level of TA, we use sodium bicarbonate; it is the only chemical which will do this without increasing the pH very much. If you need to raise the TA of your pool. Note that you should only add sodium bicarbonate at the rate of 2 pounds per 20,000 of water every 4 days.
Because  adjusting the Alkalinity level in your pool will also raise the pH level, raising the TA can be be quite a time-consuming, slow process. Lowering the total alkalinity is also a slow process. Acid, either liquid or dry, or sodium bisulphate is added to the deepest part of the pool. The acid should only be added a little at a time, diluting it before pouring it into the pool. total alkalinity test kitWait a day or so between applications. It could take several days to reduce the TA if it is very high.
Adding the pH decreaser to the pool's deep end, in one area, will increase the exchange of hydrocarbons. A general rule of thumb applies here. If you want to lower pH more and Alkalinity less, "walk your acid" around the pool. If you wish to lower the Alkalinity more, and pH less, "pool your acid" into a deep area without much circulation.
If you have a high TA, and have more questions, please visit our water balancing page.