In this post, I want to talk about some of the more unusual situations that negatively impact the action of your pool's disinfectant. You may remember that I said in an earlier post, that if you keep your pool's chlorine level at three parts per million (ppm), your pool will seldom have an algae bloom. This is because at three ppm, there is still a reserve of chlorine in your pool, a reserve that will allow for exceptional situations to occur, even ones that negatively impact the amount of existing chlorine. This way there will still be some chlorine left over to carry the pool through until the next time you can add some more. It is the same here for bromine, if you decide to use this disinfectant, you will have to keep the concentration at about twice the level, in parts per million, as you do for chlorine. So lets talk about some of the situations.
Phosphates:
High phosphate levels: Phosphate is a nutrient for algae, and when there is too much phosphate in your pool's water, you may find it difficult to keep the water clear and free from algae. Phosphates originate from many sources: bird droppings, rain runoff, agricultural fertilizers, decaying plant and animal organics, urine, and sweat.
If your pool repeatedly turns green with algae blooms, even in the presence of a rigorous disinfection program, then it is time for you to test your pool water for phosphates. Take a sample of your water to your local pool store. If it is found that your pool has a high concentration of phosphates, then also have them test your pool water for it's TDS (total dissolved solids) level too. Most likely, your water will have a high TDS reading also.
There are a couple of remedies. If it is winter, go ahead and drain the pool, and then immediately fill the pool with fresh water, you don't want to let the pool remain empty for any length of time. The second remedy is for you to use a phosphate precipitating product. This will cause the phosphates to fall out of suspension, onto the floor of the pool. Then you simply vacuum the resulting debris out of the pool. Preferably, if you can, bypass the filter, directly to waste.
If you have a pool with a multi-port valve, you can just set the dial of that valve to "waste" and the precipitate will leave the pool directly. If you don't have a multi-port valve then it still may be possible to divert the water around the filter by cutting into the pipe as it leaves the pump, and connnecting the backwash hose to this stub, and as you vacuum, the phosphate precipitate will go elsewhere instead of into your filter. Later, the pipe can be glued back together. Another option here is it install a Jandy three way valve immediately after the pump, this will give you the option to vacuum to waste whenever you want to.
Nitrates:
Nitrates are formed when nitrogen from ammonia, urine, sweat, and lawn care products combine with oxygen in the water to form nitrates, nitrates will take the oxygen out of your hypochlorous acid. This destroys the hypochlorous acid and obviously weakens your disinfection program. The solution here is to drain the pool, there is no alternative. Pool draining will be covered in a later post.
Dust Storms:
These acts of nature carry so much dirt and debris that it can completely destroy all of the chlorine in your pool! Summer dust storms are the main reason I tell prospective swimming pool owners that what they need to have is the smallest pool that they can possibly get by with, as well as the biggest pump, piping and filter that they can afford. Further more, let's go ahead a get two skimmers, a dedicated line for the automatic cleaner and design a nice oval shape for that swimming pool.
The worst situation is when the new pool owner gets saddled with a huge rectangular pool with an undersized pump, an undersized filter and undersized piping. I have noticed that large pools almost never have a corresponding increase in the size of their equipment, even though the volume of water that needs to be moved and treated, is two, three, four or more times the size of an ordinary pool.
The only way to compensate somewhat for a large pool with undersized equipment is to run the pool's pump and cleaning system much more often, perhaps even continuously during the monsoon season. The owner of this kind of large pool, at any rate, is really going to have to suffer looking at a messed up pool during most of the monsoon season, or be involved in constantly cleaning it out manually, it can get to be quite a bit of work.
The dust storms that are generated in the Phoenix area can be really huge. Just in the past week, a monster dust storm more than a mile high and 50 miles wide passed through Phoenix and most of Maricopa County. It made national and international news. You can see it on YouTube. The upshot here is that if your pool is built properly, it will be better able to take a hit from one of these monster dust storms.
If you hear about or see that a dust storm is coming in, you might as well turn the pool's pump on and add a bag of shock to the skimmer. That will help prevent your pool from greening up. If the dust storm is huge or with very high winds, then as I have said in an earlier post, you might as well turn the pool pump off, and let the dust and debris settle to the bottom of the pool before you begin any clean up efforts.
Dogs in the pool:
If you let the family dog have access to your pool, the hair from it's body will shed into the pool water, make a mess inside the skimmer and pump strainer basket, the hair will entangle itself in the pump's impeller, and any that gets into your sand filter, will likely remain there for a long time, hair doesn't backwash out easily. Mud, from the dog's paws will enter the pool and since the dog's paws will be repeatedly washed off inside the pool on the steps or love seat, the filter will get plugged up sooner. Dogs also like to urinate inside the pool. Your dog's anus will be rinsed off also.
A dog that uses the pool for it's own personal entertainment is a happy dog. The pool service professional has a different viewpoint. Everything that I have been talking about up to this point, the whole sanitation process, the cleaning and disinfection procedures, are completely negated by the swimming pool owner who thinks it's wonderful to see "little wolfie" play in the pool. Sometimes, "little wolfie" gets to play in the pool with the children, or grandchildren. A wonderful sight it is! I hope they take a lot of photos.
I will not be a party to this type of joy. If I see dog hair in my customer's pool on a regular basis, I have learned from experience, that I will probably have to let them go. Usually, they will not restrict their dog's activity. So...they will have to take care of the pool themselves, or find someone else who will. I do not want to take care of, or service a swimming pool, for the pleasure of a dog. Even if that dog is accompanied by humans. Sorry.
Of course, after I became exclusively a pool repairman, I was more than willing to fix whatever pool problems "little wolfie" was causing. But, I let the customer know what the facts were on the subject. Swimming pools in the summer are always difficult to keep sanitary under the best of conditions. Keeping your dog out of the pool is a smart thing to do. Buy your dog a large plastic pool and put it off in the corner of the yard somewhere. The dog will love it. Minimize your dog's access to your pool.
Ducks:
Ducks sometimes decide that they like a certain pool, maybe your pool. Usually, the chosen pool is surrounded by mature vegetation, giving the duck, or ducks, some cover. A swimming pool that is starting to be visited by ducks, not surprisingly, will have duck poop on it's floor, and because these birds are large, the poop will be large. Obviously, this will cause an increased need for chlorine, because poop of all kinds is about 50% bacteria. That is why those ducks need to be chased away. If these ducks are allowed to build a nest in the vegetation surrounding your pool, or somewhere nearby, they will be really difficult to get rid of.
I was called once to a home where the customer had ducks for pets, this guy thought that I should be able and willing to take him on as a customer, even though the ducks used the pool, and turned it into a green pond! Sorry, no dog pools, no duck pools. There are companies that service ponds exclusively.
If you notice duck poop in your pool and you happen to see the ducks, you are going to have try to chase them off immediately, otherwise they may get nested on your property and you may have ducklings! You may have to get used to throwing bread on the swimming pool's surface!... Quack and quack, quack!
The next post: More Negative Impactors on Disinfection
Saturday, July 9, 2011
Wednesday, July 6, 2011
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.
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.
Tuesday, July 5, 2011
Disinfection Continued
Natural Water Hardness, High Evaporation Rates and Total Dissolved Solids:
Let's explore some of the ways that water chemistry can negatively impact and modify the efficacy of disinfectants. One of the greatest issues we have here in the Sonoran Desert is a two fold problem. The first part of the problem is that the water we have is very hard. In other words, the water here has a lot of dissolved minerals in it, the the largest being calcium carbonate. It is not uncommon for calcium carbonate to come out of Phoenix's, Scottsdale's or Glendale's water system at a concentration of 300 to 400 parts per million. In addition to this, the fact is that the evaporation rate in the Phoenix area is twelve feet a year. So the water you have had in your pool last year has evaporated away, but has left behind all the minerals that it had contained.
As the water continues to evaporate and minerals continue to concentrate, the water level is maintained by the pool owner or by means of a automatic pool leveler. So highly mineralized water continues to enter the pool do to refilling activity and distilled water continues to evaporate. How does this impact the disinfection process? Well basically, it just gradually gets really difficult for the oxidizing agent to find the organic molecules. It is as though you are trying to find a friend of yours in a crowd, the larger the crowd and the more densely packed the crowd is, the more difficult it will be for you to make contact with you friend. Hypoclorous acid, in water that is highly mineralized, just keeps bumping into other stuff instead of the organic matter.
When you have for instance, a water concentration of calcium carbonate in the range of 1000 parts per million, you can assume that the actual total amount of everything dissolved in the water is approaching 2000 parts per million or more.There is a name for this "everything dissolved", it is called Total Dissolved Solids (TDS), when your pool's TDS gets too high, the chlorines ability to do its job or function can get reduced tremendously. So high TDS levels are caused by not only the hard water being added to a pool, combined with high evaporation rates (high temperatures and low humidity), but also everything else that gets put in the pool.
This includes stuff that is supposed to be in the water, like cyanuric acid (stablizer), sodium from any liquid bleach that has been used and regular sodium chloride, if you have a chlorine generator. One the other hand, left over calcium residues from shock treatments, or glue from chlorine tablets, atomized suntan oils, dissolved plaster, copper based algaecide residues, are all examples of stuff that we don't want in the water.
I knew of a man who bought or built his swimming pool in 1963, and refused to ever drain his pool. This pool had a sand filter which he obviously did backwash, so that the full effect of his situation was allevated somewhat. I first swam in his pool in 1976, and noticed an salty taste in his pool water: because he liked to use liquid chlorine as a disinfectant. The pool as the years went by became increasingly difficult to keep clear, and every summer would turn green until he whacked it back into shape. Finally an entire summer went by without his being able to turn the pool clear.
Finally, the pool turned a solid green all year and turned into a pond. Still he was not interested in draining his pool. The last straw was when the walls of the pool turned black. I was called in and drained the pool in 2008 and performed a chlorine wash. It took me about eight hours of work, but I got the pool back in shape.
The walls of the pool were layered with calcium ion scale, that was smooth to the touch, with a light grey coloring. This was caused by extremely mineralized pool water being run at a very high pH, and by using alkaline liquid chlorine without using acid on a regular basis to adjust the pH down. The only upside to this, was that his plaster, after all these years was still in surprisingly good shape, the high pH levels and scaling evidently protected the plaster from erosion.
This was the worst example, I have ever known, of allowing the TDS to increase to the point of collapsing the sanitation effort. So, as an absolutely critical part of your sanitation effort, be sure that you drain your pool often enough. I drain my pool every winter, around Christmas, during the coldest part of the year, and am happiest if I can drain the pool out on a cold rainy day. This will protect the pool's plaster from drying out and delaminating. Pool draining techniques will be covered in a later post.
Potential Hydrogen (pH) and Chlorine Effectiveness:
Another factor that impacts disinfectant efficacy and chlorine in particular is the water's pH, potential hydrogen. We can all remember the acid/base concept. Water that has a high pH, is base. Water that has a low pH, is acidic. The pH of your pools water is directly related to chlorine effectiveness.
When you pour liquid chlorine into the pool or introduce a granular chlorine or put chlorine tablets in the pool, chlorine breaks into two separate chemical forms. The first is called hypoclorous acid. Hypochlorous acid is the actual oxidizing agent that destroys organic matter in your pool. The other chemical that forms is hypoclorite ion. Hypochlorite ion does not oxidize organic material in any appreciable amount. These two forms of chlorine exist simultaneously in the water, one does the disinfecting, the other just acts as a type of reservoir for the hypoclorous acid.
The next idea is where you are going to learn to get interested in your pools pH. There is a direct relationship between the amount of hypchlorus acid and hypochlorite ion and the pH of your pools water. The higher your pool water's pH is, the less there is of hypochlorous acid in the water and the more there is of hypochlorite ion.
Remember we said that hypochlorous acid was the actual oxidixing agent? So if you run your pool with a high pH, no matter how much chlorine you put in the water, the killing ability of that chlorine is going to be diminished. Conversely, if you keep your pool's pH low, you will increase the amount of hypochlorite ion in the pools water, and it would appear that is what we want.
But things are a little more complicated than that. Like I stated previously, the quanity of the hypochlorite ion in your pool acts as a kind of reserve for hypoclorous acid, sort of a type of storage repository. As the hypoclorous acid gets used up, more is automatically made from the hypochlorite ion. If you run the pools pH down too low the amount of measured chlorine in your pool will disappear rather quickly, because hypochlorous acid is unstable and tends to gas off into the atmosphere, Hypochlorite ion in contrast is more stable, but unfortunately is not a very good disinfectant.
So the answer here is a type of compromise, where you keep the pH down but not too low. Most experts recommend keeping the pH between 7.2 and 7.6. This range will give you a sufficient amount of hypoclorous acid while also keeping a healthy reserve of hypoclorous acid in the form of hypochlorite ion. An additional benefit that accrues to you is this: by keeping the pools water to within this pH range, the minerals remain somewhat sequestered or held in the water instead of precipitating out in the form of scale onto your pools surfaces. If you let the pH move up for any extended period of time you may begin to notice that your plaster, whether it is white or black, will start to stain up. If you don't have a plaster pool, you will still accumulate staining on whatever surface you have and will have staining occurring around the pool's water line. So by keeping the pH lower you suppress two problems at once; you enhance the chlorines ability to disinfect your pool and you keep problem staining at bay.
How to adjust the pH:
When we want to lower the pH of our swimming pool's water, the proper method is to walk the acid, this is done by pouring the acid into the pool as you are walking along the perimeter of the pool. You want to have the pool pump running. As you are pouring the acid in, lean down towards the water in order to reduce the splashing of acid onto the cool deck, your skin or clothing. Sometimes the splashing of the acid can reach up to your face. So it would be a good idea to wear goggles.
The best method is to get down on your knees, and while holding onto the bottle of acid, let it float in the pool water near an water inlet and slowly pour the acid into the stream of water from that inlet. Never pour more than a pint of acid into the pool at one time. Wait a day then test the pH again then add more if needed. Oftentimes, it is only necessary to add a much smaller amount than a pint. Never pour acid onto your steps, or love seat areas, it will ruin the surface over time. Don't pour acid into just one area, will reduce the total alkalinity of the water. In the next post we will cover a situation where that is exactly what you want to do, and there will be a particular reason for pouring it into the water in that way.
Next, I am going to discuss total alkalinity and how it relates to the water's pH.
Let's explore some of the ways that water chemistry can negatively impact and modify the efficacy of disinfectants. One of the greatest issues we have here in the Sonoran Desert is a two fold problem. The first part of the problem is that the water we have is very hard. In other words, the water here has a lot of dissolved minerals in it, the the largest being calcium carbonate. It is not uncommon for calcium carbonate to come out of Phoenix's, Scottsdale's or Glendale's water system at a concentration of 300 to 400 parts per million. In addition to this, the fact is that the evaporation rate in the Phoenix area is twelve feet a year. So the water you have had in your pool last year has evaporated away, but has left behind all the minerals that it had contained.
As the water continues to evaporate and minerals continue to concentrate, the water level is maintained by the pool owner or by means of a automatic pool leveler. So highly mineralized water continues to enter the pool do to refilling activity and distilled water continues to evaporate. How does this impact the disinfection process? Well basically, it just gradually gets really difficult for the oxidizing agent to find the organic molecules. It is as though you are trying to find a friend of yours in a crowd, the larger the crowd and the more densely packed the crowd is, the more difficult it will be for you to make contact with you friend. Hypoclorous acid, in water that is highly mineralized, just keeps bumping into other stuff instead of the organic matter.
When you have for instance, a water concentration of calcium carbonate in the range of 1000 parts per million, you can assume that the actual total amount of everything dissolved in the water is approaching 2000 parts per million or more.There is a name for this "everything dissolved", it is called Total Dissolved Solids (TDS), when your pool's TDS gets too high, the chlorines ability to do its job or function can get reduced tremendously. So high TDS levels are caused by not only the hard water being added to a pool, combined with high evaporation rates (high temperatures and low humidity), but also everything else that gets put in the pool.
This includes stuff that is supposed to be in the water, like cyanuric acid (stablizer), sodium from any liquid bleach that has been used and regular sodium chloride, if you have a chlorine generator. One the other hand, left over calcium residues from shock treatments, or glue from chlorine tablets, atomized suntan oils, dissolved plaster, copper based algaecide residues, are all examples of stuff that we don't want in the water.
I knew of a man who bought or built his swimming pool in 1963, and refused to ever drain his pool. This pool had a sand filter which he obviously did backwash, so that the full effect of his situation was allevated somewhat. I first swam in his pool in 1976, and noticed an salty taste in his pool water: because he liked to use liquid chlorine as a disinfectant. The pool as the years went by became increasingly difficult to keep clear, and every summer would turn green until he whacked it back into shape. Finally an entire summer went by without his being able to turn the pool clear.
Finally, the pool turned a solid green all year and turned into a pond. Still he was not interested in draining his pool. The last straw was when the walls of the pool turned black. I was called in and drained the pool in 2008 and performed a chlorine wash. It took me about eight hours of work, but I got the pool back in shape.
The walls of the pool were layered with calcium ion scale, that was smooth to the touch, with a light grey coloring. This was caused by extremely mineralized pool water being run at a very high pH, and by using alkaline liquid chlorine without using acid on a regular basis to adjust the pH down. The only upside to this, was that his plaster, after all these years was still in surprisingly good shape, the high pH levels and scaling evidently protected the plaster from erosion.
This was the worst example, I have ever known, of allowing the TDS to increase to the point of collapsing the sanitation effort. So, as an absolutely critical part of your sanitation effort, be sure that you drain your pool often enough. I drain my pool every winter, around Christmas, during the coldest part of the year, and am happiest if I can drain the pool out on a cold rainy day. This will protect the pool's plaster from drying out and delaminating. Pool draining techniques will be covered in a later post.
Potential Hydrogen (pH) and Chlorine Effectiveness:
Another factor that impacts disinfectant efficacy and chlorine in particular is the water's pH, potential hydrogen. We can all remember the acid/base concept. Water that has a high pH, is base. Water that has a low pH, is acidic. The pH of your pools water is directly related to chlorine effectiveness.
When you pour liquid chlorine into the pool or introduce a granular chlorine or put chlorine tablets in the pool, chlorine breaks into two separate chemical forms. The first is called hypoclorous acid. Hypochlorous acid is the actual oxidizing agent that destroys organic matter in your pool. The other chemical that forms is hypoclorite ion. Hypochlorite ion does not oxidize organic material in any appreciable amount. These two forms of chlorine exist simultaneously in the water, one does the disinfecting, the other just acts as a type of reservoir for the hypoclorous acid.
The next idea is where you are going to learn to get interested in your pools pH. There is a direct relationship between the amount of hypchlorus acid and hypochlorite ion and the pH of your pools water. The higher your pool water's pH is, the less there is of hypochlorous acid in the water and the more there is of hypochlorite ion.
Remember we said that hypochlorous acid was the actual oxidixing agent? So if you run your pool with a high pH, no matter how much chlorine you put in the water, the killing ability of that chlorine is going to be diminished. Conversely, if you keep your pool's pH low, you will increase the amount of hypochlorite ion in the pools water, and it would appear that is what we want.
But things are a little more complicated than that. Like I stated previously, the quanity of the hypochlorite ion in your pool acts as a kind of reserve for hypoclorous acid, sort of a type of storage repository. As the hypoclorous acid gets used up, more is automatically made from the hypochlorite ion. If you run the pools pH down too low the amount of measured chlorine in your pool will disappear rather quickly, because hypochlorous acid is unstable and tends to gas off into the atmosphere, Hypochlorite ion in contrast is more stable, but unfortunately is not a very good disinfectant.
So the answer here is a type of compromise, where you keep the pH down but not too low. Most experts recommend keeping the pH between 7.2 and 7.6. This range will give you a sufficient amount of hypoclorous acid while also keeping a healthy reserve of hypoclorous acid in the form of hypochlorite ion. An additional benefit that accrues to you is this: by keeping the pools water to within this pH range, the minerals remain somewhat sequestered or held in the water instead of precipitating out in the form of scale onto your pools surfaces. If you let the pH move up for any extended period of time you may begin to notice that your plaster, whether it is white or black, will start to stain up. If you don't have a plaster pool, you will still accumulate staining on whatever surface you have and will have staining occurring around the pool's water line. So by keeping the pH lower you suppress two problems at once; you enhance the chlorines ability to disinfect your pool and you keep problem staining at bay.
How to adjust the pH:
When we want to lower the pH of our swimming pool's water, the proper method is to walk the acid, this is done by pouring the acid into the pool as you are walking along the perimeter of the pool. You want to have the pool pump running. As you are pouring the acid in, lean down towards the water in order to reduce the splashing of acid onto the cool deck, your skin or clothing. Sometimes the splashing of the acid can reach up to your face. So it would be a good idea to wear goggles.
The best method is to get down on your knees, and while holding onto the bottle of acid, let it float in the pool water near an water inlet and slowly pour the acid into the stream of water from that inlet. Never pour more than a pint of acid into the pool at one time. Wait a day then test the pH again then add more if needed. Oftentimes, it is only necessary to add a much smaller amount than a pint. Never pour acid onto your steps, or love seat areas, it will ruin the surface over time. Don't pour acid into just one area, will reduce the total alkalinity of the water. In the next post we will cover a situation where that is exactly what you want to do, and there will be a particular reason for pouring it into the water in that way.
Next, I am going to discuss total alkalinity and how it relates to the water's pH.
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