Pool Care Guide Chlorine



In order to Keep the pool water free from contaminants, it is necessary to add a chemical, which is capable of killing algae before it becomes visible, or a health hazard. As a rule, the presence of algae in water does not pose a significant risk to health, but it can enter open cuts or sores and cause an infection. Once the concentration of algae in the water becomes great, it is visible to the naked eye as discolored water or blemishes on the pool surface. At this stage, more drastic measures than just the routine addition of chlorine or some other water disinfectant. Approaches to visible algae control are covered in the last section of this manual. Here, the most common type of water sanitizer, chlorine, will be covered in detail, along with its testing procedures, and some troubleshooting guides.


Before discussing methods of using chlorine, some basic terms must be introduced. They will be presented in a "dictionary" format, and will include pronunciation guides when necessary.

Total Chlorine: The total amount of chlorine, in any form. Dissolved in the pool water. It is measured in parts of chlorine per I million parts of water (by volume), and the measurement is abbreviated a ppm (parts per million). Total chlorine can be tested directly with an ordinary test kit.

Combined Chlorine: The amount of chlorine in the pool water, which is chemically combined with organic waste matter. This matter need not be algae, and, in fact, could include one or more of the following: suntan lotion, body oils, sweat, and other body fluids. While these materials are organic, they do not cause visible water discoloration at normal concentrations. They do, however, prevent chlorine from effectively destroying algae. Combined chlorine is measured in ppm, but is not tested directly. To find the level of combined chlorine in the pool water, subtract the free chlorine level (see below) from the total chlorine level.

Free Chlorine: The amount of chlorine in the pool water, which is active and available to effectively destroy algae. The free chlorine level is the most important chlorine test level, and can be tested directly using a deluxe home test kit or at your nearest Pool Supply Store.

Dry Chlorine: Any form of chlorine, which is neither a liquid nor a gas. Dry chlorine is available in tablet or granular form.

Liquid Chlorine: Also known as Sodium Hypochlorite, liquid chlorine is available only in one-gallon containers, usually in cardboard boxes containing two or more gallons. Liquid chlorine should not be confused with chlorine bleach, such as Clorox, as it is several times stronger than bleach.

Gas Chlorine: Gas chlorine can either be added directly to the pool water, or it can be manufactured from ordinary salt in a chlorine generator such as the Chlorine Factory. In the long run, it is the least expensive of all three types of chlorine to use, but only the generators can be used by the pool owner. Direct injection of gas chlorine is done only by qualified and licensed pool care services. Chlorine is present in nature as a gas, and because of this it contains no fillers or by-products.


Chlorine is manufactured in three different types: dry, liquid, and gas. Dry chlorine is made both in a tablet form and granular form. Liquid chlorine and gas chlorine each are made and sold in one form. All types of chlorine, which are available to swimming pool owners, are discussed in this section.

Tablets Chlorine tablets are usually made in two different sizes: 3-inch and l-inch diameters. Both sizes are available due to the fact that each requires a different method to introduce them into the pool water.

a. 3" tablets (Jumbo Tablets) 3-inch tablets are by far the most common size of chlorine tablets. They dissolve very slowly, and are generally available at a lower cost to the customer. Both of these facts make 3-inch tablets far more cost effective than their l-inch counterparts. 3-inch tablets can be introduced to the pool in a variety of ways. They can be used in an in-line chlorinator or a floating chlorinator.

b. 1 " tablets (Tablets) l-inch chlorine tablets are smaller, and thus dissolve faster than 3-inch tablets. This is advantageous in the case where there is relatively low water circulation, or if the only available method of introducing chlorine into the pool is the floating chlorinator. Since there tends to be very little water movement in floating chlorinators, and erosion of the tablets depends on water movement, the faster-dissolving l-inch tablets would be the chlorine form of choice. Both l-inch And 3-inch tablets are made from the same type of chlorine, thus they have equal strength. The only difference lies in the size of each tablet.

** Paradise Pools™ does not recommend putting any form of chlorine in a floating basket, pump baskets, or ADR bags. Use an in-line chlorinator if installed or your skimmer basket.

Granular Chlorine

Dry chlorine is also available in granular form. The types of granular chlorine vary in strength, and care should be taken in choosing the strength that best suits the swimming pool's needs.

a. Sodium Dichlor (Pad Chem.) Sodium Dichlor is granular chlorine intended for concrete, vinyl-Lined, and fiberglass swimming pools and cold-water spas. Since it only contains 62% available chlorine, it is not powerful enough to damage these surfaces. The use of Sodium Dichlor in plaster pools and heated spas is not recommended due to the relatively higher cost involved in maintaining an ideal chlorine level.

b. Trichlor (Pad Chern. 99) NOT TO BE USED IN COLORED PLASTER OR PEBBLE TEC FINISHES! Trichlor is the most powerful dry chlorine available. It contains 89% available chlorine and also contains conditioner, which, as explained in a later section, helps to increase the life of the chlorine once it has dissolved in the water. Because of its high strength, trichlor cannot be used in vinyl-lined or fiberglass pools or fiberglass spas. If used in one of these environments, the- trichlor would damage the lining of the pool or spa, causing leakage and discoloration. However, it's higher concentration of available chlorine allows for smaller doses and longer times between applications, thus making it more cost effective than Sodium Dichlor.

c. Calcium Hypochlorite Calcium Hypochlorite is another type of granular chlorine. As its name suggests, it contains calcium, a mineral that can cause scale buildup on the tile and the pool surface. For this reason it is not recommended to use Calcium Hypochlorite on a regular basis as a primary source of chlorine. It is, however, widely used for super chlorination. This use is acceptable since super chlorination is only done periodically. However, prolonged or excessive use of Calcium Hypochlorite for super chlorination can result in scale buildup (see later section on super chlorination).

** Paradise recommends that the pool surface is completely clean before using, so as not to stain the pool surface.

Liquid Chlorine

Liquid chlorine is a very common type of chlorine used in swimming pools for super chlorination and algae removal. Because it contains only 10% available chlorine, and it contains no conditioner, it is not advisable to use liquid chlorine as a primary source of chlorine for the pool. It is, however, an excellent choice for super chlorination, as it is relatively inexpensive and dissipates within 12 to 24 hours, allowing use of the pool in a very short time. Liquid chlorine is sold only in one-gallon containers and is usually packaged with two gallons in one box. It does not have a long shelf life (about 2 weeks), and thus should not be stored for future use.

Gas Chlorine

Gas chlorine is the purest form of chlorine available. Since chlorine occurs naturally as a gas, it contains no by-products, and thus contains 100% available chlorine. Gas chlorine can be added to the pool in two ways: it can be directly injected into the pool water from a storage container, or it can be manufactured from salt using a chlorine generator. The latter method is available to the consumer, but direct gas injection can only be done by licensed pool service technicians.


In-Line Chlorinator

In-line chlorinators are those, which are installed with the piping network of the swimming pool equipment. They hold either 3-inch or l-inch tablets and have regulator valves to control the rate at which the chlorine dissolves. In-Line chlorinators allow for longer times between applications of chlorine and keep the chlorine away from the reach of children and animals.

Floating Dispenser (Not Recommended)

Floating chlorine dispensers are available in a variety of shapes and sizes, and sometimes are in the shape of decorative animals such as ducks and swans. In some cases they are pre-loaded with l-inch tablets and are disposed of when empty. Others are refillable, allowing the use of either 3-inch or l-inch tablets. In some cases, the chlorine demand for a certain pool is greater than the output of a single floating chlorinator. In . these special cases, the best alternative is to use more than one floater, or to use the faster dissolving l- inch tablets.


Contrary to some opinions, the pool's skimmer is a perfectly acceptable place for chlorine tablets. The high water flow in the skimmer provides excellent erosion of 3-inch tablets, and the plastic construction of today's modem skimmers is not subject to corrosion by chlorine. In addition, PVC pipes, thermoplastic pumps, and fiberglass filters do not corrode in the presence of chlorine. However, copper heating elements and other metal objects found in some pool filtration systems may be corroded and have decreased life due to high concentrations of chlorine. In these cases, it is advisable to use one of the other two methods described above.

* * Paradise recommends never putting any form of chlorine in a floater, pump baskets or the ADR bags. Use an in-Line chlorinator or put them in the skimmer basket.

Direct Application

Direct chlorine application applies only to granular and liquid chlorine use. The only way to add granular or liquid chlorine to the pool water is to evenly sprinkle it over the water surface. Because of the harmful fumes and chlorines tendency to irritate skin, granular and liquid chlorines are generally rejected in favor of tablets.

Chlorine Generator

An alternative to directly adding chlorine to a pool using either tablets or granular chlorine is to generate the chlorine from ordinary salt, which is made from sodium and chlorine. Two methods are most often employed. The first is to add salt pellets into a chamber of a special chlorine-generating unit, such as the Chlorine Factory. The salt is mixed with water and a small electric current separates the sodium from the chlorine. The chlorine is injected into the pool through a series of hoses, and the sodium is kept in a separate chamber for later disposal. After about 2 weeks, the sodium is removed and more salt is added. The other method involves the addition of granulated salt directly into the pool water. As it circulates through the filtration system, a special unit adds a small electric current to the mixture and the sodium and chlorine are separated and added simultaneously to the water. There is no sodium by-product to remove, and a small amount of salt is added to the pool about twice a year.


In order to ensure the proper amount of chlorine is in the pool water, the water must be tested regularly. It is assumed that at least a standard pool water testing kit is present and that the instructions for the particular kit have been read and understood.

The Chlorine Scale

The concentration of chlorine in water is measured in parts per million (ppm), that is, parts of chlorine per one million parts of water. A standard test kit is graduated on one side from zero ppm to 3.0 ppm, although the concentration can be much higher than 3.0 ppm. Once the chlorine vial in the test kit is filled with pool water, and the proper number of drops of OTO (or tablets of DPD, for those test kits using such a chemical) are added to the sample, the color of the sample should change in the presence of chlorine. That is, if chlorine is present in the pool water, the color of the sample should change to a shade of yellow (or pink DPD test tablets are used). The next step is to match the color of the sample with one of the colors corresponding to the chlorine concentrations on the test kit. If the color of the sample matches that of one of the concentrations on the test kit, the number corresponding to that color is the amount of TOTAL chlorine in the swimming pool (in the case DPD test kits. the color of the sample after adding DPD #1 is the FREE chlorine, and the color after adding DPD #3 is the TOTAL chlorine).

Ideal Levels

Most test kits are labeled with an "ideal" level for chlorine, usually between 1.0 and 1.5 ppm. While this level is adequate for most pools, it is recommended to maintain a higher chlorine concentration than this during the hot summer months often experienced in Arizona. It has been found that a concentration of 1.5 ppm dissipates too quickly during days with temperatures above.

Type Of Chlorine Used Type Of Dispensr Used Recommended Starting Amount
3" Tablets Floater Fill floater and open wide
  Skimmer 2-3 tablets per 10,000 gallons. (Summer)
1-2 tablets per 10,000 gallons. (Fall,winter, spring)
  In-Line Chlorinator Fill chlorinator and set wide open
1" Tablets Floater Fill floater and open at least halfway.
  In-Line Chlorinator Same as for 3" tablets
Granular Direct Application 3/4 cup per 1 0,000 gallons.
Chlorine Generator   Set to "high".


95-1000P, thus it is recommended that a concentration of 3.0 ppm be maintained during the warmest summer months. This ensures that the minimum level of 1.5 ppm is present and also provides additional chlorine to combat the additional organic wastes present due to the increased pool use. Due to the fact that each swimming pool has different chlorine requirements, it is difficult to recommend the precise number of tablets, etc, that are required to maintain a 3.0 ppm chlorine level. Par this reason, it is advised to experiment with a particular pool to determine its requirements. As a starting point, use the guide above.

Allow the system to circulate for 24 hours, and then test the chlorine concentration. If the level is too high, decrease the amount of chlorine used, or decrease the setting of the chlorinator (i.e. Close floater slightly, or set generator to "med", etc.), If the level is too low, add more tablets or granular chlorine, add another floater, or supplement using an additional method (i.e. use the skimmer and a floater, etc.).

Time And Frequency Of Testing

During the summer months, a swimming pool must be tested at least once a week, since the levels of chlorine and pH can vary dramatically within a matter of hours. Since the chlorine and pH are the two tests of primary interest, these are the only two, which must be tested on a daily basis. The other tests, such as alkalinity, hardness, etc., are tested on a weekly and/or monthly basis, as discussed in later sections. As the outside temperatures decrease, the frequency of testing can decrease also. In other words, during non-summer months, testing for chlorine and pH can be done twice per week or even once per week in the coldest winter months.

During the middle of the afternoon, the temperature is warmest and the sun is usually able to shine into the water easiest, and it is at this time that algae grows most rapidly. Thus, this is also the time when the chlorine level should be at its highest, since it will be necessary to prevent the rapid spread of algae. It is for this reason that it is recommended to test the pool water during the warmest part of the day (i.e. between the hours of 3:00 pm and 5:00 pm). If the chlorine was tested at 9:00 in the morning, and the level is 3.0 ppm, it is entirely possible that the chlorine concentration may decrease dramatically, say to 1.0 ppm before the warmest portion of the day arrives. Therefore, an ideal chlorine level in the morning may not necessarily mean an ideal level in the afternoon, when it is needed most. If an ideal 3.0 ppm level is noticed at 5:00 pm, it can be assumed that it was at least that amount throughout the day, and the pool was properly protected against the spread of algae.


Super chlorination refers to a process by which the chlorine level in the swimming pool is raised to abnormally high levels over a very short period of time, usually a few hours. Since this requires rapid addition of chlorine, slow-dissolving tablets are not suitable for super chlorination. Instead, special granular or liquid chlorines are used which are packaged in appropriate sizes and which do not remain in the pool water for an extended period of time, allowing the pool to be used as soon as possible. Another common mime for super chlorination is "shocking".

Reasons For Super chlorination

Over time and with extended use, organic wastes build up in the pool water. These wastes include body oils, sweat and other body fluids, and suntan lotions. Once these wastes are present, the chlorine begins to break them down, as it would any organic substance, which enters the water. However, since the chlorine is working to eliminate these organic wastes, it is not available to eliminate spores of algae as they enter the water from the air. This can allow the algae spores to multiply, resulting in visible algae in a short period of time. It is therefore required to increase the pool's chlorine concentration rapidly in an effort to eliminate the organic wastes so that the chlorine is free to prevent the spread of algae.

Types of Super chlorination Treatments

There are three basic methods of super chlorination. Shock-It, a convenient, one-pound package of chlorine has been formulated for this purpose. It is unstabilized, so that the pool can be used for swimming in a short period of time. One disadvantage of Shock-It is that it contains calcium, the main contributor of hard water, and because of this it is not recommended for use in pools with hard water (see Section 6 of this guide). As a rule one-pound bag of Shock-It is used for every 10,000 gallons of pool water. Liquid chlorine can also be used to superehlorinate a swimming pool. As with Shock-It it is unstabilized, but in addition, it contains no calcium, and as a result it can be used in areas where hard water is a problem. Generally, 1 gallon of liquid chlorine is needed for every 10,000 gallons of pool water. In addition, swimming pools can get the effect of super chlorination with out the use of a chlorine product. "Non-chlorine shock treatments", as they are called, add active oxygen to the pool water in a granular form, They are generally non-toxic and non-irritating and thus the pool can be used as early as 10 minutes after application. This method is usually about twice the cost of standard chlorine-based super chlorination treatments, and one pound will treat 25,000 gallons of pool water.


It is recommended to super chlorinate a swimming pool every two weeks in the summer, when the pool is used more, and the possibility of the presence of organic wastes is great. During the off-season, once per month is sufficient. It is also recommended that super chlorination take place in the evening, after the sun has set, since this is when the pool is not being used and the treatment will not be removed by UV rays from the sun before it has the opportunity to perform its function.