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What is Chlorine Demand?

Chlorine demand is defined as the inability to maintain a chlorine residual in a pool or spa even after repeated application of a chlorinating product. There are a great number of substances that can contribute to chlorine demand. These include (but are not limited to) bacteria, algae, ammonia, urine, sweat, health and beauty products, bather waste, and animal waste. These contaminants can enter the water in many ways, such as source water, rainwater, bathers, animals, fertilizers, plants/leaves, and industrial pollution.

Unfortunately, there is no easy cure for many chlorine demand situations. In most cases, there are still only two options. The first is to apply the appropriate amount of chlorinating product (as determined through testing by bringing in a water sample to Advanced Spa And Pool), and the second is to replace some of the water with fresh water that has no chlorine demand. If you chose to replace water, we recommend bringing in a sample of the source water for testing to make sure the source water does not also have chlorine demand. In situations where the chlorine demand is accompanied by very cloudy water, a treatment with a flocculant may reduce the demand by physically removing some of the contaminants from the water. This doesn’t cure the demand, but can possibly lessen it. It will be necessary to have a chlorine demand test done again in this case. *Flocculants can ONLY be used in pools that are equipped with a filter that has the ability to vacuum to waste. This is imperative to the treatment process.

Keep timing in mind when you are treating chlorine demand…it’s important. Checking the chlorine residual a few hours after treatment could show the presence of free chlorine, and you might assume the demand is broken. However, if slow-reacting contaminants are present, the chlorine can be used up as they continue to react. As a result, the chlorine residual will end up at zero as more time passes, which means that the demand is not truly broken. This is why it’s very important to add the entire amount of recommended product as instructed, continue to test frequently, and be sure the free chlorine residual holds at 1 – 4 ppm for a full 24 to 36 hours.

Of course, the best course of action is always prevention. Keeping on a weekly maintenance routine that includes routine oxidation or “shocking” as well as an application of a maintenance algicide will help keep pool water clear and free from contaminants that can contribute to chlorine demand. It is also important to know when additional oxidation is needed. Most pool care systems recommend a once per week application of an oxidizer, but there are instances where more frequent addition is needed. These include after a party, rain, warmer than normal temperatures, and any time there is suspected contamination of the pool water (such as fertilizer or pollutants). Stop by and talk to the Water Care Experts at Advanced Spa And Pool to determine the best course of action to keeping your pool clean and clear.

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Written by Advanced Spa And Pool


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