How to Cure Chlorine Demand or Chlorine Lock

Are you frustrated that the chlorine readings on your pool aren’t where they should be even after adding plenty of chlorine or doing a shock treatment? This problem is called chlorine demand or chlorine lock. We can help you solve this problem.

What Causes Chlorine Demand

Chlorine demand occurs when there are a lot of organic and inorganic chemicals, minerals and other types of matter in swimming pool water that the chlorine is struggling to neutralize. These contaminates force the chlorine in your pool to work overtime. It can also occur when phosphates and nitrates get into the swimming pool water.

There are three common circumstances that create these conditions:

1. Heavy Rainfall

Heavy rainfall can cause chlorine demand if the rainwater that falls into your pool is full of particulates or chemicals. It introduces large amounts of contaminates that the chlorine has to fight.

2. Months Without Treatment

Leaving your pool untreated and unattended for months can also create the conditions for chlorine demand. When leaves and debris breakdown in water, they add nitrogen and other organic contaminates. This is why many pool owners notice this problem when they re-open their pool in the spring. Properly cleaning and prepping your pool at the end of swimming season can prevent this problem.

3. Runoff from Household Cleaners or Fertilizer

If you use household chemicals or fertilizers with phosphates and nitrates around your pool, these chemicals can get into your pool from rainwater runoff or cleaning. These chemicals make it harder for chlorine to do its job and cause chlorine demand. This is why it is a good rule of thumb to keep all fertilizers and non-pool-friendly chemicals far from the swimming area.

How to Cure Chlorine Demand?

The only way to cure chlorine demand is to give your pool the chlorine that it needs through consistently shock treatments. A general rule to follow is to use 3 pounds of calcium hypochlorite pool shock for every 10,000 gallons of pool water. This may vary depending on the degree of chlorine demand that your pool has.

Before you go to the store and stock up on chlorine shock treatments, you should do a Chlorine Demand test to determine how much chlorine your pool needs.

When you do the pool shock treatment, make sure that the cyanuric acid (chlorine stabilizer) levels are between 30 and 80 ppm. Wait until the sun goes down to do the treatment. The sun eats up chlorine.

The Difference Between Chlorine Demand & Chlorine Lock

Many people use the terms chlorine demand and chlorine lock interchangeably. Chlorine lock can also refer to the belief that chlorine stabilizer inhibits chlorine from doing its job. There is no evidence to support this theory. Most pool experts agree that chlorine lock is not a real issue. If someone tells you that your pool is suffering from chlorine lock, it is a good idea to ask what they mean.

If your pool has chlorine demand, give us a call! We can test the chlorine levels of your swimming pool and tell you the accurate amount of chlorine that your pool needs. We can also take care of the shock treatments for you.