Lesson 3 - The Water

    Water has been called the Great Dissolver for its ability to dissolve so many different elements. Acidic water dissolves things like paint, plaster and metal much faster than non-acidic water. This is important because you control what the pH of your pool's water will be. 

    Water's dissolving capabilities explain several bad things that happen to pools. No matter what your pool's design and construction, the water which is central to the reason you have a pool in the first place, is the pool's own worst enemy. Left alone and given enough time, the water in a pool would ultimately destroy the pool. 

    Added to the problem of dissolving, water's capacity to erode makes it a formidable foe indeed. Water eroded the Grand Canyon, so it can certainly handle the tile grout and plaster in your gunite pool. There are few materials that water cannot eventually destroy. The materials your pool is made out of (i.e., concrete, vinyl, fiberglass, steel, paint, plaster) are no match for water. You can slow down the process of destruction by maintaining an ideal chemical balance, but you can't stop it. Let's talk a bit about balancing chemicals, or water chemistry as it's generally known.

    If you ask most pool owners what is the most important chemical reading they take with their test kit, they usually respond 'Chlorine'. Occasionally they say 'pH' is more important. Both answers are incorrect in my view. While it is true that pH is more important than chlorine, the pH is determined by the Total Alkalinity. So that makes total alkalinity (or T/A for short) the most important reading of all. 

    Why do I say pH is more important than chlorine? By any criteria you care to name, the pH level affects the water and your pocketbook more than the chlorine level. Consider this. What is the worst thing that can happen if your chlorine level gets too low? The pool can turn green and it could cost you $200 clean and clear the pool. But if the pH level gets too low, it can cost 10 times that to replace a vinyl liner or a heater, and 20 times that amount to resurface a plaster pool. If the chlorine is allowed to get too high, it will burn your eyes and dry your skin. But if the pH gets too high, it can form scale and ruin your heater, or form calcium bumps on plaster which can only be removed by sanding the entire surface of the pool. Thus from a cost analysis, pH is more of a concern than chlorine.

    The pH is more important than chlorine also because the pH determines how effective the chlorine will be. If the pH goes above 8.0 the chlorine's effectiveness will be significantly decreased. As the pH gets lower, the chlorine becomes more effective. That's why if we are fighting algae in a pool, we try to keep the pH as low as possible without going below 7.0 which is neutral. And you know how people always blame chlorine for burning their eyes when they swim? Guess what... pH can burn your eyes too. The pH of the fluid that bathes your eyes is 7.4, so if the pH of the pool water is too high or too low, your eyes will burn. When it comes to water, pH is everything.

    So why do people give chlorine a higher status than pH? My theory is that chlorine is something you can see, taste and smell. While pH, on the other hand, is an abstract concept about how acidic the water is. You cannot tell just by looking that the pH of your pool is high or low. But if the pool is green, you can be sure the chlorine is too low. In other words you can see the results of a chlorine imbalance fairly quickly in the form of cloudy water, algae growth, chlorine odor and so on. As a result chlorine often gets blamed for problems it didn't even cause, like burning eyes or water discoloration. 

    I've tried to establish that pH is more important than chlorine, against popular opinion. Now I want to press my luck and claim that Total Alkalinity or T/A is more important than pH. This is because total alkalinity determines what the pH will be. If the T/A is high, the pH will be high. If the T/A is low, the pH will be low. 

    Here's another correlation between pH and total alkalinity. If pH is hard for some people to grasp, T/A is almost impossible to grasp because it is even more abstract. So let's keep it simple. There are four things you need to know about total alkalinity, and they are:

1. Total Alkalinity tells the pH what it is going to be, either high or low (high is non-acidic or base, while low is acidic or corrosive). 

2. Total Alkalinity determines how easily the pH can change. If the T/A is high, pH resistance to change will be high; if T/A is low, pH will change easily (up or down).

3. Total Alkalinity is lowered with acid (either dry acid or liquid muriatic acid), and T/A is raised with ordinary baking soda (such as Arm & Hammer bicarbonate soda).

4. There is a formula for how much baking soda to add to raise the total alkalinity of pool water. The formula is: 3 lbs. of baking soda raises the T/A of an average size pool (i.e., 20,000 gallons) by 10 ppm (parts per million).

    Here's one more thing about T/A before we move on. I have seen a few cases over the years when the pH and the T/A diverge. In other words, it is possible that the pH can be high while the T/A is low and vice versa. What do you do if this occurs? If the pH is high (say, 8.0) while the T/A is low (say, 30 ppm) I would do nothing for a week or two to see if things stabilize. If the readings persist, I'd add acid to lower the pH first. But beware that it might lower the T/A also. Once the pH is ok, then add baking soda until the total alkalinity comes up to normal. 

    What is normal? Not what most books say. Most books say that T/A should be 80 to 100 ppm. In my experience, if you raise the T/A that high, the pH will go above normal. So I'd recommend 60 ppm as acceptable for a plaster pool, and 80 for a vinyl, painted or fiberglass pool. Your water may vary, so check with your local pool professional.

    Now suppose that the pH remains low, even after you get your alkalinity in the ok range. I've seen this happen once or twice with fiberglass pools. If this is the case, you may add a cup of soda ash (sometimes called pH up) which will raise just the pH and not the T/A. Let me quickly add a caution about soda ash.

    In the old days, soda ash was the preferred way to raise pH. People bought it in 100 lb. sacks. Some old timers still sell it that way. It is usually sold as pH up. The problem is that soda ash only works on the pH and not the T/A. As I've said earlier, the T/A controls what the pH will be, so if you ignore the T/A you'll never get your pH right. Once upon a time I added soda ash to a pool and watched horrified as the water turned an ugly greenish gold color right before my eyes. The water had turned metallic. In other words the dissolved metal in the water precipitated into solid form (more about dissolved metal in a moment). 

    It took two weeks to turn the water back to normal. I haven't carried soda ash on my truck in 15 years. That's how little it is used. Soda ash is a harsh chemical that most pools never need. If you have some, I urge you to give it to someone you don't like. Let them add it to their pool, while you stick with the more friendly baking soda. Baking Soda (also known as bicarb) works on the cause of a low pH by raising the Total Alkalinity. The only time you need to add soda ash is in the instance outlined above, and then only in very small quantities.

    Speaking of dissolved metals in the water brings us back to the first point I made about water being the great dissolver. Dissolved metals is one of the most difficult problems pool owners encounter. There are chemicals to help control this problem, but they are not always effective. In our discussion of water, I will share my struggles with dissolved metals so you can have the benefit of my experience.

    All water has metal in it. You normally can't see it because it is dissolved. Students in college science classes perform a laboratory experiment in which they lower the pH of water to dissolve a piece of metal, then raise the pH back up to make the metal precipitate into solid form. The same thing can happen in your pool, but it's the kind of experiment you don't want to perform. 

    Normally in a pool we try to keep the metal in dissolved form. When the metal becomes visible it usually is an unsightly brown stain that forms on the walls and floor. The iron that causes such staining can be from underground pipes that carry fresh water, or from natural sources. Metal stains can also be blue/green when the cause is copper. Copper can give the pool a nice deep blue color and help fight algae. But the source of the copper is often the pool's heater which has soft copper pipes, and that's not good. Also, some older pools have copper pipes before PVC was available. 

    When the pH gets too low the water becomes corrosive and strips away the inside of the metal pipe making it thin. The metal then is deposited in the pool as a dissolved solid. You can take a water sample to your favorite pool store and have it tested to see how much metal is in the water. If the amount of metal is low, the metal will stay dissolved as long as the pH is in the normal range (7.2 - 7.6). But if the amount of metal reaches a higher level, you may have to use chemicals to keep the metal in a dissolved state. Once the concentration of metal gets too high, no amount of chemicals will keep the metal dissolved. In that case, water must be taken out and replaced by fresh water, thereby diluting the concentration of metal to a level that can be controlled.

    If you have a stain in your pool and want to know if it is caused by metal, here is a simple test you can perform. Take a vitamin C tablet and rub it on the stain. If the stain goes away it is metallic and may respond to metal treatment. If it persists, then it may be organic and will have to be removed some other way. Vitamin C is sold in pool stores as ascorbic acid and works great to remove metal stains, but it has the drawback of neutralizing chlorine, so be careful you don't trade one problem for another. Also note that a stain remover does not really remove stains, it simply dissolves the metal back into the water so that you can't see it. The water can only hold so much metal though, and the stains can quickly return. There is a liquid stain remover that helps hold the metal in suspension. It can be used alone or in conjunction with ascorbic acid.    

    If there is one pool problem that regularly vexes new pool owners, it's metal treatment. Don't be surprised if your local pool store is little help. It is a problem that is not well understood, often misdiagnosed, and hard to control even for professionals. In Lesson 8 - Prevention I discuss how to (and whether to) prevent metal stains.

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