Total Alkalinity

Total Alkalinity (TA) as it concerns us, is composed of mostly dissolved carbon dioxide, carbonates, bicarbonates, and hydroxide. It naturally occurs in rain runoff traveling over and through rock formations containing these substances. It is of interest to us because the amount of TA in your swimming pool's water is a direct measurement of the ability of that water to hold it's pH steady.

This is known as the water's buffering capacity against pH changes. Because of the TA's composition, it has acid neutralizing abilities. The higher the amount of TA in the water, as measured in parts per million (ppm), the more resistant that water is to changes in pH. The lower the amount of TA in the water, the less resistant that water is to pH changes.

If the TA of your pool's water measures between 80 and 120 ppm, your pool's water is in a state where if you add some acid, the pH will move down somewhat, and if you add some soda ash, the pH will move up somewhat. This gives you the proper amount of control over your pool's pH. Between these two values, 80 ppm and 120 ppm, is where you want the TA to be.

If you test the water for TA and the result is higher than 120 ppm, then you will find it difficult to move the pH up or down, even with the addition of substantial amounts of acid or soda ash. Conversely, if you test the water and the result is lower than 80 ppm, you will find the pH will move too easily up and down with the addition of just a little acid or soda ash. This is not good because, this indicates the pH is not stable. For instance, if, after you add a little acid to your swimming pool's water, in order to move the pH from say, 7.8 to 7.2, all is not well, because after a day or two, you will be surprised to find that the pH is back up to 7.8.

It is also annoying when after you add soda ash, in an attempt to raise the pH from 7.0 to 7.6, you find that upon the next pH test, the pH is back down too low. A negative aspect to a low TA is that the water is much more corrosive to the walls and floor of the pool, no matter what they are constructed of. A low TA combined with a low pH, will degrade your pool's plaster and concrete, strip copper from the the heater, discolor the chrome guard rails, and corrode any exposed metal in the pump. With this in mind let us see what corrective measures there are.

How to Adjust Total Alkalinity:

If you find after testing your water,that your swimming pool's water has a TA above 120 ppm, then you are going to want to use the following technique to move the TA down. Turn the pool off, and after and hour or so, the water will stop moving. Take a bottle of muriatic acid, and step up onto the diving board. Pour approximately one pint of the acid into the center of the pool. If you have a small pool, use a lessor amount. If you have a large pool, still use a pint of acid and see what happens first. After you pour the acid in: DO NOT TURN THE POOL PUMP ON! You want a low pH cloud to form in the center of the pool and to remain there, this will cause some of the carbonates within the low pH cloud to gas off as carbon dioxide. This will lower your TA. You may have to repeat this process every couple of days in order to move the TA down into the desired range, be patient it may take a couple of weeks.

If you find that your swimming pool's water has a TA below 80 ppm, then you are going to want to use the following technique to move the TA upwards. Add a box of baking soda (sodium bicarbonate) wait two or three days, test the water again. Repeat if necessary, notice that both techniques are time consuming. We don't want any surprises!

Don't do as one customer did, and put twenty pounds of baking soda into the pool all at once! The baking soda caused a purple sludge to precipitate out, which came to a rest at the bottom of their pool! I asked them, why would they do that?... "Because the guy at Paddock pools told us to! It was on a computer readout!" I looked at that readout and that is what it said. It was probably a typo of some sort, I'm sure that it was meant to be two pounds. Even so, the readout should have indicated that the addition of twenty pounds of baking soda should have been done within a time frame of weeks.

I don't like to follow formulas like: "because of this reading, you have to add so much of that" I don't go for that. Depending on what the test results are: just add a little of something to get some change, and then see what happens, then if necessary add a little more. Avoid big trouble. Remember when I said that small deviations call for small corrections, and big deviations always call for big, expensive, time consuming corrections? Well, I added some extra words this time. But, always test things out on a small scale first, if you screw up its' no big deal, just a small screw up. This idea of "testing things out on a small scale, can be applied in many other areas of life.

We have been concerned with TA because of it's relationship to pH and the influence that pH has on chlorine's effectiveness. All the dots connect!

The Next post will cover the more exotic negative impactors on the disinfection process.