Combined Chlorine (CC) is the exhausted portion of chlorine that has bound to organic contaminants and is no longer actively cleaning your pool. High levels of CC cause skin irritation, cloudy water, and the classic, overwhelming “chlorine odor.” Eliminating it is essential for a truly fresh and healthy swimming environment.
Most people believe that a strong chemical smell means a pool has too much chlorine. The truth is exactly the opposite. That smell is the unmistakable signal that your pool actually needs a massive dose of fresh chlorine. Understanding how chlorine becomes “combined” is the secret to getting rid of the odor and the irritation it causes.
How Chlorine Becomes Combined
When you add chlorine to your pool, it starts out as Free Chlorine (FC). This is the active, powerful sanitizer waiting to do its job.
When a swimmer enters the water, they bring organic contaminants with them, such as sweat, body oils, cosmetics, or urine. The Free Chlorine attacks these organics and binds to them to neutralize the threat. Once this chemical bond happens, that portion of chlorine is considered “spent.” It transforms into Combined Chlorine (CC), also scientifically known as chloramines.
These chloramines are practically useless for sanitizing. Worse, they are highly volatile and easily gas off into the air just above the water line, creating that pungent, eye burning smell often associated with poorly ventilated indoor pools.
Calculating Your Combined Chlorine
To find out if you have a chloramine problem, you need to test your water. Standard test strips are often not precise enough, so you need a high quality DPD drop test kit.
The test will give you two numbers: your Free Chlorine (FC) and your Total Chlorine (TC). Total Chlorine is simply the sum of both the active and the spent chlorine.
Therefore, to find your Combined Chlorine, you just subtract the Free Chlorine from the Total Chlorine. Ideally, your CC level should be zero, but anything over 0.2 ppm means it is time to take action.
Key insight: If your Total Chlorine reads 3.0 ppm, but your Free Chlorine is only 1.0 ppm, you have 2.0 ppm of Combined Chlorine. That is a massive amount of exhausted waste floating in your water.
How to Eliminate Combined Chlorine
You cannot simply wait for chloramines to go away on their own. To destroy Combined Chlorine, you have to break the chemical bonds holding it together.
This is done through a process called breakpoint chlorination. You must add a massive, overwhelming dose of unstabilized chlorine (pool shock) to raise your Free Chlorine level to exactly ten times the amount of your Combined Chlorine.
- Calculate the Dose: If you have 0.5 ppm of CC, you need to add enough shock to raise your FC by 5.0 ppm.
- Shock at Night: Add the shock in the evening so the sun’s UV rays do not burn off the active chlorine before it can destroy the chloramines.
- Leave the Cover Off: The destroyed chloramines need to physically gas off and escape into the atmosphere. If you leave a solar cover on the pool, the gas will become trapped and the smell will remain.
Prevent Chloramines with DualPool
Constantly shocking your pool to eliminate chloramines is expensive and forces you to stay out of the water for days at a time. The smarter strategy is to remove the organic contaminants before the Free Chlorine ever has to fight them.
By dropping the DualPool 2-in-1 Pool Clarifier into your skimmer basket, its advanced formula actively gathers the sweat, body oils, and fine debris suspended in your water. By grouping these contaminants into larger clumps, DualPool allows your filter to physically trap and remove them. This protects your Free Chlorine, preventing chloramines from forming in the first place and ensuring your pool never develops that harsh chemical smell.
Frequently Asked Questions (FAQ)
Is it safe to swim if Combined Chlorine is high?
It is not recommended. If your Combined Chlorine is above 0.5 ppm, the water will likely cause red, stinging eyes, dry skin, and respiratory irritation. It also means your active sanitizer levels are struggling, making the water unsafe from bacteria.
Does a strong chlorine smell mean the pool is clean?
No. A perfectly clean, well balanced swimming pool has almost zero chemical odor. A strong smell is the definitive sign that the pool is full of chloramines (Combined Chlorine) and needs to be shocked immediately.
Can UV systems or ozone generators reduce Combined Chlorine?
Yes. Secondary sanitation systems like UV light and ozone generators are excellent at breaking down and oxidizing chloramines. However, they only treat the water as it passes through the plumbing, so you still need a strong Free Chlorine residual in the main pool body to keep the water safe.