Pool Water Chemistry

How many gallons of water does your swimming pool hold?

This can be a very easy or a very tough question depending on your point of view. It is without a doubt, though, an extremely important question. It is nearly impossible to add proper dosages of swimming pool chemicals to your pool if you do not know its capacity. A small above ground pool may hold 5,000 gallons of water while a large inground pool may hold more than 40,000 gallons. A proper dosage in one pool will definitely not be a proper dosage in the other. For your convenience, a gallonage chart for the most popular pool sizes is given below. If your pool size is not shown, use the listed formulas.

Above Ground Pools

48″ Wall Height 52″ Wall Height 54″ Wall Height
NOTE:
Pools with 8′ walk in stairs add 360 gallons.
Pools with 12′ radius walk in stairs add 520 gallons.
By knowing your pool’s capacity, you will have one half of the information that you need to properly add swimming pool chemicals to the pool.
Pool Size Gallons Pool Size Gallons Pool Size Gallons
12′ Round
15′ Round
18′ Round
3,186
4,978
7,169
12′ Round
15′ Round
18′ Round
3,398
5,310
7,646
12′ Round
15′ Round
18′ Round
3,568
5,576
8,029
20′ Round
21′ Round
24′ Round
8,732
9,757
12,744
20′ Round
21′ Round
24′ Round
9,440
10,408
13,594
20′ Round
21′ Round
24′ Round
9,912
10,928
14,273
27′ Round
28′ Round
16,129
17,346
27′ Round
28′ Round
17,204
18,502
27′ Round
28′ Round
18,065
19,428
30′ Round
33′ Round
19,913
24,094
30′ Round
33′ Round
21,240
25,700
30′ Round
33′ Round
22,302
26,985
11′ × 25′ Oval
11′ × 30′ Oval
12′ × 24′ Oval
6,817
8,181
7,236
11′ × 25′ Oval
11′ × 30′ Oval
12′ × 24′ Oval
7,370
8,844
7,718
11′ × 25′ Oval
11′ × 30′ Oval
12′ × 24′ Oval
7,738
9,286
8,104
15′ × 24′ Oval
15′ × 25′ Oval
15′ × 30′ Oval
9,045
9,422
11,306
15′ × 24′ Oval
15′ × 25′ Oval
15′ × 30′ Oval
9,648
10,050
12,060
15′ × 24′ Oval
15′ × 25′ Oval
15′ × 30′ Oval
10,130
10,553
12,663
18′ × 33′ Oval
18′ × 38′ Oval
18′ × 40′ Oval
14,924
17,186
18,090
18′ × 33′ Oval
18′ × 38′ Oval
18′ × 40′ Oval
15,919
18,331
19,296
18′ × 33′ Oval
18′ × 38′ Oval
18′ × 40′ Oval
16,715
19,248
20,261

Inground Pools

Pool Size Gallons Pool Size Gallons
21′ × 21′ Patio
26′ × 26′ Patio
11,070
14,910
16′ × 32′ Oval
18′ × 36′ Oval
20′ × 40′ Oval
17,540
21,420
27,860
16′ × 28′ Jewel
16′ × 32′ Jewel
16′ × 36′ Jewel
18′ × 38′ Jewel
18′ × 42′ Jewel
11,716
16,566
18,108
21,239
21,550
17′ × 33′ Grecian
17′ × 37′ Grecian
20′ × 36′ Grecian
20′ × 40′ Grecian
17′ × 39′ Grecian L
20′ × 44′ Grecian L
19,538
21,213
23,623
26,670
22,594
28,870
16′ × 32′ Keyhole
18′ × 36′ Keyhole
20′ × 40′ Keyhole
11,200
15,150
21,600
16′ × 30′ Kidney
18′ × 36′ Kidney
20′ × 38′ Kidney
14,900
20,145
20,883
20′ × 32′ Mt. Lake
20′ × 37′ Mt. Lake
21′ × 40′ Mt. Lake
24′ × 44′ Mt. Lake
13,300
17,400
19,600
24,400
16′ × 34′ × 25′ Lagoon
18′ × 37′ × 29′ Lagoon
20′ × 42′ × 31′ Lagoon
14,800
22,100
26,850
12′ × 24′ 2′ Radius Rect
16′ × 32′ 2′ Radius Rect
16′ × 36′ 2′ Radius Rect
18′ × 36′ 2′ Radius Rect
18′ × 43′ 2′ Rad L
18′ × 26′ × 37′ 2′ Rad L
20′ × 40′ 2′ Radius Rect
8,840
19,365
20,961
23,803
26,439
26,624
30,875
16′ × 35′ Roman
16′ × 37′ Roman
18′ × 39′ Roman
18′ × 41′ Roman
20′ × 41′ Roman
20′ × 43′ Roman
18′ × 44′ Roman L
19,817
19,883
24,623
24,689
28,987
29,053
25,520
16′ × 32′ 4′ Radius Rect
18′ × 36′ 4′ Radius Rect
20′ × 40′ 4′ Radius Rect
18′ × 43′ 4′ Rad L
19,046
23,500
30,557
26,123

Formulas to Calculate Pool Gallons:

Rectangular Pool: Length × Width × Avg Depth × 7.5
Round Pool: Diameter × Diameter × Avg Depth × 5.9
Oval Pool: Length × Width × Avg Depth × 6.7

Testing Your Pool Water

While your pool’s capacity is extremely important to know, it is also important to know what the chemical levels are in the pool. Pool care with proper chemical levels in the pool helps ensure that the water is invitingly clear, clean, and healthy. When the chemical levels in a pool are in their recommended ranges, the water is said to be balanced.

To save time and money, there is no more important thing that you can do than to test your pool’s water. It is regular water testing that helps ensure water that is of exceptional quality. Failure to test the pool chemicals on a regular basis will almost assuredly result in extra work and expenditures for you. Pool care with regular water testing should be looked at as an investment in fun and not as work. Without a doubt, most pool water chemistry problems are directly attributed to the pool owner failing to take a minute or two each day to test their pool’s water. In order to test the pool water, we recommend the use of test strips. Test strips give better test readings than most of the test kits which use liquid drops. For complete instructions on how to use test strips, see the test strip container.

Chemical Levels

Once you have learned how to use the test strips to test the pool water, you will probably wonder what it all means. What is the significance of the chlorine, pH, and total alkalinity readings that you have obtained? Well, it’s water chemistry time. But please, if your reaction here is to stop reading, don’t. We will keep this as simple as possible.
At this time, let’s look at the items that make your pool water clean and balanced. We will look at them one at a time and will also look at their relationship to other chemicals. (Note, pools using Baquacil, Nature 2 or other non-chlorine water treatment systems should refer to their respective user’s guide for complete instructions and information on these alternative sanitization systems.)

Chlorine

Far and away the chemical that is most closely associated with swimming pool maintenance is chlorine. Chlorine, in its natural state, is a gas. For home swimming pools, it is common to find chlorine in liquid, granular, and tablet forms. The job of the chlorine, as you are probably aware, is to disinfect the pool water. Clean pool water is not only free of debris that you can see, but it is also free of bacteria which you cannot see.

Another function of chlorine is to act as an oxidizer. In this capacity, the chlorine breaks down wastes that are brought into the pool by wind, rain, and swimmers. This oxidation process “burns out” small organic debris that are too small to be filtered out.

When chlorine is added to the pool, it forms what is called FREE CHLORINE. Free chlorine is the form of chlorine which can perform the sanitizing and oxidizing functions. As the free chlorine reacts with bacteria and algae, it is depleted. (Sunlight and heat likewise cause the chlorine to deplete from the water.) Also, as the free chlorine reacts with dirt, human waste, fertilizers, etcetera, it forms what is called COMBINED CHLORINE. (Combined chlorine is also called chloramines.) This combined form of chlorine is a much less effective form of sanitizer. As the combined chlorine builds up, swimmers will notice increased eye and skin irritation as well as a strong chlorine odor. While free chlorine is desirable and needed, combined chlorine is nothing more than a problem causer. The amount of free chlorine plus the amount of combined chlorine equals what is called TOTAL CHLORINE.

Total Chlorine = Free Chlorine + Combined Chlorine

Because chlorine can be either free or combined, it is important to know what form your test kit is testing. If your test kit uses a solution labeled Orthotolidine, or OTO for short, it is testing the total chlorine level in the pool. This reading may or may not be useful depending on how much combined chlorine is in the water. (Remember, free chlorine is useful, but combined is not useful. The problem with a total chlorine reading is that it doesn’t decipher between combined and free.) More useful to the pool owner is either test strips which check for free chlorine or a test kit which uses a reagent called DPD on the chlorine test. DPD kits can give both free chlorine and total chlorine levels. When a test strip or kit tests for free chlorine, the pool owner gets a much more accurate indicator of the “health” of their pool. (For complete testing information, refer to your test kit or test strips.)

Now that you have a better understanding of chlorine and the forms that it can take, how do you maintain proper chlorine levels in your pool, and what are the proper chlorine levels? The recommended chlorine levels are as such:

Free Chlorine: 1.0 to 3.0 Parts Per Million
Combined Chlorine: Under 0.3 Parts Per Million

When chlorine levels are not kept in the recommended ranges, the following problems can occur:
Chlorine Level Problem
Free Chlorine Too Low
  • Inadequate disinfection
Free Chlorine Too High
  • Chlorine is wasted, hence wasted money
Combined Chlorine Too High
  • Irritation to swimmer’s eyes and skin
  • Strong smell of chlorine
  • Bacteria and algae can thrive

In order to raise the free chlorine level in any pool, you simply add chlorine to the water. The hard part here is really more a matter of deciding what chlorine product to use. Pleasure Pools recommends SPARCO Slow Dissolving Tablets for daily chlorination. The reason for this recommendation is that slow dissolving tablets need to be added less frequently than fast dissolving tablets, granular chlorine, or liquid chlorine. Large slow dissolving tablets may need to be added only a couple of times per week, while other products may need to be added on a daily basis. Since pool sizes, weather, and usage all affect chlorine usage, it is impossible to say how many tablets you will need weekly. The safest way to know when and how much chlorine to add is by testing on a regular basis and then adding chlorine based on the test readings, your pool’s size, and the label’s instructions. A simple test holds the key to your pool’s water quality, and there is no substitute for it.

An even better way to chlorinate your pool is to use a SPARCO Automatic Water Treatment System. This chlorinator can be easily added to most swimming pools. The SPARCO Automatic Water Treatment System is desirable because it allows you to handle the chlorine less often, making things safer and less time consuming. Because this system can hold a large amount of chlorine tablets, you may only need to replace the treatment chamber every three to five weeks. (Actual time may vary due to pool size, weather conditions, usage levels, and other factors.) Since the chlorinator is dispensing chlorine over a long period, the pool owner is better protected against drops in the chlorine level that lead to algae and cloudy water.

Another advantage of the SPARCO Automatic Water Treatment System is that it can save money. Money is saved because as the weather changes, you adjust how much chlorine is dispensed into the pool. With most other chlorine products, you cannot control their dispersal into the pool. Over the course of the season, you will save time and money as well as reduce the chances of water problems by using this system. (For more information , please contact an Pleasure Pools representative.)

Now that we’ve examined free chlorine, combined chlorine, and chlorinating your pool on a regular basis, we can look at what to do when the combined chlorine level builds up in the pool. Remember, combined chlorine levels over 0.3 PPM are undesirable. Over time, this level will build up despite how well you keep up on adding chlorine to the pool. In order to bring the combined chlorine level down, you must add a larger than normal dose of chlorine. This dose of chlorine is called shocking, or super chlorinating the pool, and it is 3 to 5 times the normal dose of chlorine. A weekly shock treatment will destroy chloramines, human waste, algae and bacteria.

To shock your pool, Pleasure Pools recommends using one gallon of liquid chlorine per 10,000 gallons of pool water.

Gallons Liquid Chlorine = Gallons Pool Water / 10,000

For example, on a 24′ pool, shock with 11/3 gallons of liquid chlorine.

11/3 gallons = 13,600/10,000

Shock treatment is recommended at least once per week, but in extremely hot weather with a lot of use, or in rainy weather more frequent shock treatments may be needed. If at anytime the chlorine level drops to zero, shock the pool immediately as the chlorine level may actually be below zero. (This is referred to as chlorine demand.) When the weather is hot, a chlorine level of zero can result in a cloudy or green pool within 24 hours. If your pool ever gets a bad algae problem, you may be instructed to use a heavier and more frequent dosage of shock. Your shock treatments will be more effective if you add the liquid chlorine in the evening hours, when the sun will not burn it out so quickly. (Sunday evenings are a great time to shock pools since the pool has normally had a weekend of heavy use.) After shocking the pool, please allow enough time for the chlorine level to drop back down to its normal level before allowing swimmers to use the pool. If the pool needs to be shocked and used immediately, we recommend that you use a non-chlorine shock treatment product called SPARCO Quick Acting Super Shock. (An Pleasure Pools representative can give you all of the details on this product.)* Please be aware that chlorine, when used or handled improperly, can be very dangerous in any of its forms. Always read the label of any chemical that you are using, and keep all swimming pool chemicals out of the reach of children. Store in a well ventilated area away from other chemicals or direct heat. NEVER mix chemicals together.

pH

pH is not as familiar to most people as chlorine is, but it is just as important. pH is a measure of whether something is acidic, basic, or neutral, and it is always measured on a scale of 0 to 14. Everything has a pH value associated with it. A pH of 7.0 is neutral, a pH under 7.0 is acidic, and a pH over 7.0 is basic.

pH is important to swimming pool water for many reasons, and as such, it cannot be neglected without problems occurring. On a swimming pool, the pH should be kept in the following range:

Recommended pH Range – 7.2 to 7.6

If the pH is not kept in the proper range, the pool owner may experience the following problems:
pH Level Problem
pH Too Low
  • Corrodes surfaces and equipment
  • Wrinkles and fades vinyl liners
  • Increases chlorine consumption
  • Irritates swimmer’s skin and eyes
pH Too High
  • Scales pool surfaces and equipment
  • Contributes to cloudy water
  • Drops efficiency of chlorine
  • Irritates swimmer’s skin and eyes

Of the problems associated with an improper pH, the one that should be of the most interest to the pool owner is the drop in the efficiency of chlorine at a high pH. It is not uncommon when we perform water tests to find pools’ with a pH of 8.0 or above.

Unfortunately, at this pH level, the chlorine level must be kept 2 to 3 times higher in order to achieve the same sanitizing level as is achieved at a pH of 7.2 to 7.6. The result is that the pool owner either wastes money by having to keep the chlorine level at an elevated level or their pool water turns cloudy or green. Neither scenario is necessary or desirable.

The pool’s pH is crucial, and luckily, fairly easy to test for and adjust. All swimming pool test kits should test for pH, and by now, you’ve probably become familiar with how to use your test kit or strips. Once you have tested the water and obtained your results, you can make any needed adjustments to the pH.

If the pH tests low, you will use SPARCO pH Plus. To determine how much pH Plus to add, you will need to know your pH test results and your pool’s capacity. The label on the container of pH Plus will then instruct you on how much product to add.

If the pH tests high, you will need to add SPARCO pH Minus or Muriatic Acid. SPARCO pH Minus is a granular product where as Muriatic Acid is a liquid product. (For safety reasons, pH minus is normally the preferred product to use.) To determine how much pH Minus to add, carry out the same procedure as described for a low pH. When adding pH Minus or acid, never add it through the skimmer, and choose an area away from metal ladders or other metal components. For you and your family’s safety, always wear protective goggles and gloves when handling muriatic acid. Wash any spills off of clothing or pool decking and equipment immediately.

TOTAL ALKALINITY

No discussion of pH would be complete without looking at total alkalinity. Total alkalinity is a measure of alkaline materials in the pool water. While this doesn’t mean much to most of us, what is important is that these alkaline materials play a significant role in helping to maintain the pool’s pH. These alkaline materials help prevent changes in the pool’s pH. At proper total alkalinity levels, the pool’s pH will be more stable. This stabilizing is referred to as buffering the pH.

On vinyl lined swimming pools, the total alkalinity should be kept at the following levels:

Total Alkalinity – 80 to 150 Parts Per Million

In the event that the total alkalinity is out of range, the following problems may occur:
Alkalinity Level Problem
Total Alkalinity Too Low
  • pH is difficult to maintain – it drifts
  • Corrodes surfaces and equipment
  • Stains pool surfaces
Total Alkalinity Too High
  • pH is difficult to adjust – it remains fixed
  • Scales pool equipment and surfaces
  • Makes water cloudy
  • Since pH stays high, sanitizer efficiency drops

Depending on your test kit, you may or may not be able to test for total alkalinity at home. If you can’t test total alkalinity at home, bring us a water sample three or four times during the season and we’ll test it for you.

Pools with low total alkalinity levels need SPARCO Alkalinity Plus added to them. This product is a powder and is very easy to add. For the proper dosages, see the container’s label.

High total alkalinity pools require SPARCO pH Minus. You will need to use the dosage as recommended on the container.

In the event that the pH and total alkalinity both need adjusted, always adjust the total alkalinity first since this acts as a buffer for the pH.

CALCIUM HARDNESS

Calcium hardness is a measure of dissolved calcium in the pool’s water. For the most part, calcium hardness is not an item that the pool owner needs to monitor continuously. Having Pleasure Pools check the water several times a year is sufficient in most cases. The reason for not needing to have this tested as often is because it does not change near as quickly as the chlorine, pH, and total alkalinity do.

The calcium hardness should be kept in the following range:

Calcium Hardness – 120 to 300 Parts Per Million

If the calcium hardness is out of range, the pool owner may see the following problems:
Hardness Level Problem
Calcium Hardness Too Low
  • Corrodes pool equipment
Calcium Hardness Too High
  • Makes water cloudy
  • Scaling may form on equipment and surfaces

Since calcium hardness will usually be tested at our store, any recommended action , if needed, will be prescribed when we test the water.

Specialized Chemistry Considerations

Even the best cared for and “balanced” pool will need a few other chemical additions to its water to keep things looking clean and clear. The swimming pool industry refers to these other chemicals as “specialty chemicals.” These specialty chemicals help reduce overall chemical usage as well as maintenance time.

Cyanuric Acid

Of all the specialty chemicals, cyanuric acid is among the most important. Cyanuric acid is important to the pool owner because its use can help reduce the use of chlorine. Cyanuric acid, which is also called stabilizer or conditioner, helps to reduce the rate at which the sun depletes the free chlorine in the water. By slowing the depletion rate, less chlorine will be used. Since chlorine is the biggest chemical expense that a pool will have, it makes sense to make sure your pool is stabilized. The cost of stabilizer will be made up for in chlorine savings.

Many forms of chlorine have stabilizer built into them, requiring the pool owner to only have to establish the initial cyanuric acid level. Once this level is established, a stabilized chlorine will be able to maintain this level unless significant amounts of new water are added.

The recommended cyanuric acid level is as such:

Cyanuric Acid – 30 to 125 Parts Per Million

The result of too low or too high of a stabilizer reading are:
Cyanuric Level Problem
Cyanuric Acid Too Low
  • Increased chlorine consumption
Cyanuric Acid Too High
  • Chlorine becomes locked

Historically, we do not see many cases where the stabilizer level is high enough to cause the chlorine not to work, but it can happen if not enough fresh water is added to a pool over time.

For the most part, test kits designed for home use do not test cyanuric acid. Cyanuric acid is easily tested for on our professional equipment, and we will be happy to test your pool’s water anytime that you have questions or concerns. After we have the test results, we will advise you whether or not SPARCO Chlorine Conditioner & Stabilizer needs to be added.

Algaecide

When you look at pool problems, the most common one is without a doubt, algae. There are several reasons for this problem being so widespread. The first reason is improper maintenance. Inadequate chlorine levels, improper water balance, and improper filtration can all play a part in the growth of algae. Because algae can develop in such a short time, the importance of regular testing cannot be stressed enough. A couple of minutes can save you countless hours and dollars. But more importantly, the small time investment keeps your pool fun.

The second reason why algae is such a common problem on swimming pools is that algae is a very tough and resourceful plant. Algae is a primitive plant, so it is definitely not a new problem. While proper chlorine and pH levels will go a long way towards preventing algae growth, there will be times that for one reason or another, the water chemistry is not exactly where it needs to be. It is for this reason that SPARCO Algae Destroyer should be used on a regular basis. Algae Destroyer is a broad spectrum algaecide which not only kills algae, but also helps to prevent its emergence. The use of Algae Destroyer gives the pool owner another line of defense against the most common pool problem. On a weekly basis, you should add 4.3 to 8.6 ounces of Algae Destroyer per 10,000 gallons of water. For convenience, we recommend adding Algae Destroyer each week when you shock your pool.

If your pool does get algae, the first thing that you will need to do is to check and to adjust the water balance. The pool should then be shocked and a dose of Algae Destroyer added. (See dosage rate on Algae Destroyer for a pool with visible algae growth.) It is important that these treatments begin as soon as possible due to the speed with which algae can grow. Also, algae is easier to kill when it is immature. The longer algae is left untreated, the more of it you will have, and the harder it will be to kill. During treatment for algae, the filter should be run continuously until the problem is remedied.

METAL REMOVERS

Depending on the source water for the pool, metals may be present in the water. Testing for these metals will be done by your pool dealer, as few home test kits will test for them. (The most common metals tested for are copper and iron.) If metals are found in your water, an Pleasure Pools employee will instruct you on how to handle them. If these metals are not removed or made “inactive”, they can potentially cause staining.

Important Note: If your pool’s water turns colored the first time chlorine is added, it is probably due to metals in the water. The chlorine oxidizes the metals which leads to the discoloration. To remedy this problem, bring a water sample to Pleasure Pools and we will analyze the water and make recommendations on what steps will need to be taken. Fortunately, this is a very uncommon problem.

WATER CLARIFIERS

While algae is the number one pool water problem, cloudy water is not far behind. In fact, in most cases of heavy algae growth in a pool, the pool will go through a cloudy phase either before green is visible or after the green is gone. (Note, cloudy water can have causes other that algae, but proportionately, algae is the number one cause of cloudy water.)

In the early stages of algae growth, it is quite common for the pool walls and bottom to get “slimy” while the actual water begins to turn cloudy. If not shocked and balanced quickly, the pool water will quickly progress to green. If at anytime you see cloudy water developing, immediately check the pool’s chemical levels. In most cases, the chlorine level will be very low. The quicker the pool is shocked and balanced, the better the likelihood that a major algae problem can be avoided.

Cloudy water is also a very common problem after a pool has had a major algae problem. The reason for this cloudiness is that after the pool has been shocked and treated with algaecide, the algae may be killed, but it just won’t disappear. The dead algae remains in the pool water leaving a milky or cloudy appearance. These dead algae cells are very difficult to filter out due to their extremely small size. When you are fighting a major algae problem, you should expect to see the water go from dark green to light green to cloudy. As you see these changes taking place, you will know that the algae is being killed.

As was mentioned, dead algae is very difficult to filter out. In order to help the filter, clarifiers are used. Clarifiers work by taking small particles and helping to clump them together so that they are easier to filter. Clarifiers come in varying strengths, and for extremely cloudy pools we recommend SPARCO Crystal Clear. In some cases a clarifier will not be strong enough to do the job, and in these cases SPARCO Super Floc should be used.

In the event that your pool has a clarity problem, Pleasure Pools will be happy to test your pool’s water and make recommendations on the proper steps to take to remedy the problem. Our hope is that with this manual and with our personalized help, we can help you maintain your pool so that you never need to worry about cloudy water problems.

CHEMICAL SUMMARY

If you test your pool on a regular basis, paying close attention to the water’s chlorine and pH levels, pool problems will be minimized. The vast majority of pool water problems are created when the chlorine level is allowed to drop below its acceptable level. When you add in improper pH levels, problems soon develop. A couple minutes investment on your part to test the water will pay huge dividends in time, fun, and money. The other chemical levels and chemical additions are important, but the chlorine and pH levels are absolutely crucial.

Water Test Summary
Test Range
Free Chlorine 1.0 – 3.0 ppm
Combined Chlorine < 0.3 ppm
pH 7.2 – 7.6
Total Alkalinity 80 – 150 ppm
Calcium Hardness 150 – 300 ppm
Cyanuric Acid 30 – 125 ppm
Metals 0 ppm