The debate over using liquid chlorine vs. the powder form is always a concern for owners and operators of pools and spas. There are positive aspects to each product. Depending on what source you consult, you can be told conflicting information. The most important factor is that you choose your product based on the specific needs of your equipment and budget.

Basics of Chlorine describes chlorine as the "sanitizer/disinfectant/oxidizer that is most widely used by pool owners to kill any bacteria, living organisms, ammonia or other contaminates that are present in water." It is produced by the electrolysis of saltwater and is effective by breaking through the cell walls of microorganisms such as algae and oxidizing them. Chlorine is unstable and will continue to break down once produced until it is ineffective. Chlorine is also a hazardous material, and needs to be handled very carefully.

Chlorine Use and Monitoring

Chlorine is the safest and most inexpensive way to keep pool and spa water sanitized. Organisms and bacteria are constantly present in water and pose a health risk as well as an aesthetic problem. Chlorine is the tried and true method of controlling these situations. To effectively use chlorine, its level must be constantly monitored in the water because the weather, amount of microorganisms, temperature, use and other factors will cause it to fluctuate continually. Testing kits are readily available where you purchase the chemicals needed to stabilize the water and should be used according to instructions. Chlorine, no matter the form, is only as effective as its proper use allows.

Liquid Chlorine

Liquid chlorine is made by bubbling the gas form of chlorine through caustic soda, as described on It has a high pH level (around 13) and can be poured directly into the pool, but it is recommended to be added in a peristaltic pump for even distribution. Liquid chlorine use is dominant in large commercial pools because it can be delivered in 55 gallon drums and added in bulk. For residential use, the cost can outweigh its efficiency, the amount of acid needed to counteract its high pH and the difficulty in use. Liquid chlorine is less expensive than other forms. It is highly corrosive, which is a factor that should be considered.

Powder Chlorine

The common form of granular chlorine is called di-chlor, or sodium dichloro-s-triazinetrione. It's lower pH of about 7 means less acid is required to balance it. It dissolves rapidly and begins working on contaminates immediately, but only contains about 62 percent actual chlorine per pound. It contains cyanuric acid, which makes it more stable, and this product can be used as a shock treatment. Di-chlor as a treatment can be very expensive. There are two other forms of granular or powder chlorine called hypochlorites–lithium hypochlorite and calcium hypochlorite. Lithium has only 35 percent available chlorine per pound and its pH of 11 means use of acid to balance is necessary. Its advantages are it dissolves very fast before hitting the pool bottom, reducing the chances of bleaching effect for vinyl pools, it has less calcium and does not contribute to water hardness. It is also dust free and non-flammable. Cal-chlor is available in both powder and tablet form and, at 65 percent available chlorine, is a popular shock treatment product. It has a high pH of 12, but its inexpensive price makes it a popular product, even though it is unstable and breathing its dust is highly dangerous.

Making the Decision

Whether to choose liquid chlorine or powder or which is the better choice greatly depends on how it will be used. Liquid would be an obvious choice for a large institution, but may be prohibitive for a residential homeowner. The variances in pH levels, available chlorine per pound and the equipment it will be used in come into play. Keep in mind the needs and budget allowed, and choose based on these factors.