How do different types of chlorine differ and which ones are suitable?
Different types of chlorine have the same goal, for sanitation, but they have different properties and impacts on the water, so they should be chosen according to their use.
Chlorine is used to maintain chlorine levels and for water shocking. Maintaining chlorine levels involves gradually adding chlorine to the water to keep the free chlorine value between 1-3 ppm at all times, for sanitation purposes.
Water shocking, on the other hand, involves adding a large amount of chlorine at once to create a shock or superchlorination, which requires a chlorine concentration in the water of at least 10 ppm to eliminate the used chlorine.
For saltwater pools, which already have a chlorine generator for maintaining chlorine levels, if it doesn't produce quickly enough to shock the water, additional shock chlorine may need to be added.
Chlorine can be divided into stabilized and unstabilized types. Stabilized chlorine contains cyanuric acid, which is like a sunscreen protecting chlorine from being destroyed by sunlight, and should be at an appropriate level. Having too much cyanuric acid reduces the efficiency of the chlorine.
Unstabilized chlorine does not contain cyanuric acid. If this type is used in outdoor pools, additional cyanuric acid should be added.
There are many types of chlorine, and we will compare the five most commonly used ones: chlorine tablets, granular shock chlorine, flake chlorine, shock chlorine flakes, and liquid chlorine.
1. Chlorine tablets, or Trichloroisocyanuric acid (TCCA) 90%
Chlorine tablets, or Trichloroisocyanuric acid (TCCA) 90%, come in 3-inch and 1-inch tablets and are used for maintaining chlorine levels. They can be put in the filter basket or easily tossed into a chlorine floater.
The advantage is that they dissolve slowly, gradually adding chlorine to the water, so you don't have to add it every day. One tablet can last 5-7 days, making it a popular choice. It's suitable for homes, resorts, hotels, and it's also stabilized, containing cyanuric acid to protect against sunlight, so there's no need to add extra cyanuric.
This type of chlorine may slightly lower the pH, but not significantly. However, pH levels should be measured regularly.
2. Shock chlorine tablets
Sodium Dichloroisocyanurate, also known as "shock chlorine tablets", is typically used for shocking water due to its rapid dissolving nature. They can be added to the filtration basket or simply tossed into the pool, where they create fizzing bubbles and dissolve in a few minutes, causing an immediate increase in chlorine levels.
This type is popular for water shocking due to its easy usage (just count the tablets) and the fact that it doesn't contain calcium, which prevents the formation of scale when used regularly. It can be used in both saltwater and chlorinated pools. However, using this type of chlorine will increase the level of cyanuric acid in the water.
3. Flake or powdered chlorine
Trichloroisocyanuric acid (TCCA) 90%, also known as "flake or powdered chlorine", is the same type of chlorine as tablet chlorine, but in a flake or powder form. It's used to maintain chlorine levels, but the application is slightly different from tablet chlorine.
Because of their shape, flakes and powders have a larger surface area exposed to water and dissolve faster than tablets. Therefore, you need to adjust the amount properly and add it to the pool daily.
The advantage of this type is that it can be added in more precise amounts than tablets. It also contains cyanuric acid to protect against sun damage and is cheaper than tablets. It's suitable for large pools or pools with daily maintenance.
4. Shock granular or powder chlorine, Calcium Hypochlorite.
"Shock granular or powder chlorine", or Calcium Hypochlorite, is used for shocking water just like the tablet chlorine but is a different chemical type. Besides the granular or powder form that differentiates it from tablets, this type of chlorine is unstabilized, meaning it doesn't contain cyanuric acid.
The absence of cyanuric acid isn't necessarily a disadvantage because high cyanuric acid levels can decrease the efficiency of chlorine, and it may also lead to scale formation. If the water already has high levels of cyanuric acid, using an unstabilized type of chlorine might be more appropriate.
This type of chlorine contains calcium, which increases the water hardness level. Hardness should be kept within the appropriate range. Low hardness can lead to corrosive water that can damage materials the water touches, while high hardness can cause scale formation. Therefore, this type of chlorine isn't suitable for saltwater pools as it can lead to scale formation within the chlorine generator.
This type of chlorine is suitable for occasional use or for shock treatments aimed at killing scale, as it has high efficiency in killing scale without adding cyanuric acid.
5. liquid chlorine
Sodium hypochlorite, also known as "liquid chlorine" or "chlorine water", can be used for both maintaining chlorine levels and shocking the pool.
For maintaining chlorine levels, the appropriate amount should be added daily, and cyanuric acid should also be added if the pool is outdoors.
Liquid chlorine has the least impact on other water parameters, including not increasing cyanuric acid or hardness levels. It may slightly increase pH, but the level will return to normal once the chlorine starts working.
Liquid chlorine is popular for large pools and pools with daily maintenance because it is inexpensive. However, precise calculations for its usage may be required because of its short shelf life.
This article does not suggest that one type of chlorine is the best, but it outlines the properties and impacts of each to guide in making the most suitable choice. Regardless, regular measurement of chlorine, pH, cyanuric acid, alkalinity, and hardness is recommended.