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Sanitizer Selection and Routine Testing

Platinum PoolCare Aquatech, Ltd.

Photo courtesy of Platinum PoolCare Aquatech, Ltd.

How does chlorine work as a sanitizer, oxidizer, and shock?

Chlorine controls bacteria and viruses, which is an important part of preventative water care. Used on a regular basis, chlorine is both a sanitizer that kills algae and bacteria, and an oxidizer that removes unwanted organic matter, such as oil and sweat. Chlorine levels should be kept at 1 – 4 ppm in pools. (Though not commonly used in spas, the ideal chlorine level is 3 – 5 ppm in spas.) Chlorine also functions as a shock when used in large doses of 10 ppm; shocking or superchlorinating is necessary if there is a major drop in stabilizer levels or if you see algae growth.


 To prevent chlorine from being burned off by sunlight, cyanuric acid (a stabilizer) must be added to the water. Stabilized chlorine already contains cyanuric acid and comes in the forms of dichlor, which is usually granular, and trichlor, typically a stick or tablet suitable for floating erosion feeders or filter baskets. When using unstabilized forms of chlorine—most commonly a granular form called cal-hypo—cyanuric must be added separately, and should be kept at 25 – 50 ppm in pools.


What are my options in non-chlorine sanitizers?


Bromine is another popular sanitizer, particularly for spas because it’s more suitable for warm, turbulent water. Though it dissipates in sunlight, spas are covered on a regular basis, meaning bromine is kept in spa water quite easily. Bromine does not create the odors sometimes associated with traditional sanitizers and works over a wider pH range. Additionally, bromine does not irritate the skin and eyes, which makes it a great option for some pool owners.


A second chlorine alternative is biguanide. Biguanide-based systems are typically sold as a set (a sanitizer, shock, and clarifier) that must be used together. When used properly, biguanide provides a soft, silky feeling to the water. It also prevents the fading of swimsuits.


Systems that release natural minerals into the water, reducing (but not eliminating) the need for a chemical sanitizer, may also be considered. Typically, mineral systems are sticks or cartridges that slide into the core of a pool’s or spa’s cartridge filter. As the water passes through, it picks up the minerals. Mineral systems can leave skin feeling softer than chlorine alone.


Ozone can also reduce the need for other chemicals. Simple ozone generators have become standard equipment for hot tubs, while ozone systems for swimming pools are more complex. See Automatic Options for more information on automated forms of water care.


What levels do I have to check and how often?


Sanitizer, pH, total alkalinity, calcium hardness, and total dissolved solids (TDS) levels should be checked regularly. Together with temperature, these factors all contribute to water balance. Balanced water is healthy water, which means contaminants (bacteria and algae) and scale are under control, staining potential is minimized, and the water looks clean and inviting.


The proper ranges are:


  • Free available chlorine (FAC) 1 – 4 ppm (in pools), 3 – 5 ppm (in spas)

  • Bromine 4 – 6 ppm

  • Biguanide 30 – 50 ppm

  • pH 7.2 – 7.8

  • Total alkalinity 80 – 120 ppm

  • Calcium hardness 200 – 400 ppm (pools), 150 – 250 ppm (spas)

  • TDS under 1,500 ppm


How often to test greatly depends on bather load and the weather, since hot, humid conditions promote algae growth. In general, you should check the sanitizer and pH levels every day. Total alkalinity and calcium hardness should be checked at least weekly, and the other factors monthly. More frequent checks may be needed in heavily used pools.

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