Pool care and maintenance is a task that faces all pool owners, including keeping the pool water sanitized. Not only is unsanitary water cloudy and uninviting, it is also potentially dangerous. Unsanitary pool water can lead to a variety of bacterial illnesses, intestinal and respiratory infections, diarrhea, ear infections and more.

Although maintaining pool water sanitation may seem daunting at first, it is actually easy once you know the basics. By understanding how swimming pool chemicals work, and following a few simple steps each week to maintain the health of their pool water, owners will find it easy to keep their pool water clean and enjoyable.

What Pool Chlorine Does

Before discussing how to administer pool chlorine, it will help to have a basic understanding of how it works in pool water. When chlorine dissolves in water it changes to form hypochlorous acid (HOCI) and hypochlorite ions (OCI). Hypochlorous acid is the primary active ingredient in pool water sanitation. When we test for Free Available Chlorine (FAC) this is what we are reading. We manage the FAC to ensure the pool water is safe to swim. Hypochlorous acid combines with any organic matter and/or bacteria and destroys them.

Once destroyed, the organic matter, bacteria, ammonia and nitrogen compounds combines with the chlorine, which causes the chlorine to become relatively inactive and ineffective. This inactive chlorine, changes to form other compounds including chloramines, which builds up in the pool, but does little to aid sanitation. Pool owners must regularly remove the build-up of chloramines. If they are not removed through shocking (oxidation), chloramines prevent proper sanitation and become a primary cause of cloudy pool water.

Pool Water Shocking with Chlorine 

Super chlorinating the pool water is a process commonly referred to as “shocking” the water. The build-up of chloramines are effectively removed by adding a large amount of granular pool chlorine, achieving a chlorine test level at least 5 – 10 parts per million (PPM). This super-chlorination will remove or oxidize the excess contaminants and chloramines.

Administering regular shock treatments is necessary in order to maintain basic sanitation levels. It is a good idea to designate a particular day of the week to perform the chlorine shock treatment so that it becomes a part of your regular routine.

How Much Chlorine for Your Swimming Pool

Since pool chlorine is available in different strengths, the type of chlorine you choose will affect the amount required. Chlorine brands try to distinguish themselves by touting certain advantages of their product over their competitors' products, but the truth is that most chlorine for swimming pools is equally effective. However, your personal preferences and pool type might lead you to choosing one type of pool chlorine above another. Here is a look at some of the most popular types of chlorine on the market.
  • Trichlor: Pool chlorine tablets and sticks are Trichloro-S-Triazinetrione (Trichlor) is available in 84-90% concentrations. Placed in the floating chlorine feeders and chlorinators, Trichlor automatically and gradually dissolves into the pool water. The tablets are available in 1” or 3” sizes; the 1” tablets dissolve faster than the larger 3” tablets or the larger sticks. Trichlor is Stabilized chlorine, which means that the chlorine has Cyanuric acid added to help prevent the ultraviolet rays of sunlight from prematurely destroying the chlorine in water. One more note on Trichlor: although some people add the Trichlor tablets or sticks into the pool skimmer baskets, this is a bad idea. Since all chlorine is acidic and very corrosive, it can easily harm skimmer baskets, pool pumps, filters and eroded away metal pool heater components.
  • Dichlor: Sodium Dichloro-S-Triazinetrione (Dichlor) is available in 56 – 62% concentrations. Chlorine Dichlor is a granular form of Stabilized chlorine that is pH neutral and does not have to be pre-dissolved. Dichlor is a convenient option that allows for precise control over chlorine levels in the pool. Dichlor has the advantage of not harming pool liners or pool and spa surfaces. However, the disadvantage of Dichlor is that the pool water must be tested more frequently and additional chemical added daily for proper sanitation.
  • Calcium Hypochlorite: Another granular form of chlorine, calcium hypochlorite (Cal-Hypo) is not stabilized and available in concentrations between 65 – 78%. Dissolve granular Cal-Hypo in water prior to use to prevent bleaching or harming of pool components. It is a great oxidizer and a good option for shock treatments. Like Dichlor, calcium hypochlorite also allows for precise control over chlorine levels. The major disadvantage of calcium hypochlorite is that pool water must be tested more frequently and additional chemical added daily for proper sanitation.
Chlorine Stabilizer Cautions

Dichlor and Trichlor have Isocyanuric acid (Cyanuric acid) incorporated because of its ability to help stabilize chlorine against damage from sunlight. However, a high Cyanuric acid (CYA) level, especially above 60 parts per million compromises the effectiveness and the oxidation-reduction potential (ORP) of chlorine. If you choose stabilized pool chlorine, CYA will build-up quickly. For every 10 parts per million (PPM) of Free Available Chlorine added using Trichlor, CYA increases by 6 PPM and Dichlor increases by 9 PPM. You will need to test and monitor the chlorine stabilizer CYA level diligently to ensure the level does not get too high. Many pool owners develop chlorine effectiveness issues because if this. To lower the CYA level you must replace existing pool water with fresh water.

The alternatives to swimming pool chlorine containing Cyanuric acid are sodium hypochlorite (liquid pool bleach) and granular calcium hypochlorite. These pool chemicals do not contain chlorine stabilizer and therefore do not have the disadvantage of CYA mentioned above, but they do increase the pH.

Swimming Pool Chlorine Tips
  • Stabilized 3” chlorine tablets are the most popular and least expensive form of pool chlorine. When properly used, 3” tablets may not need attention for a week or more. Test the pool water at least weekly.
  • 1” chlorine tablets are well suited for use in automatic chlorinators, above ground pools, small in-ground pools, and spas.
  • Granular chlorine is very effective, but it requires a higher level of chemical maintenance.
  • Liquid pool bleach is good for pool shock and daily pool sanitizing without raising Cyanuric acid levels. The downside is possible chemical leaking during transport and the potency diminishes significantly within a few months.
  • You should keep pool chlorine test levels between one to three parts per million at all times. By maintaining that level, your pool will stay in top form throughout the swimming season.