If you keep adding chlorine to your pool only to test it a day or two later and find the chlorine level low again, you’re not alone. During the hottest part of a San Jose summer, pools can use chlorine much faster than expected.

But continually adding more chlorine isn’t necessarily the solution.

If your pool won’t hold chlorine, something is consuming it, destroying it, or preventing you from maintaining the correct active chlorine level. Finding the cause can save chemicals, prevent algae and keep your pool clear and safe.

1. Summer Sunlight Is Breaking Down Your Chlorine

Sunlight—specifically ultraviolet (UV) radiation—breaks down free chlorine in outdoor pools.

This is where cyanuric acid (CYA), commonly called pool stabilizer or conditioner, becomes important. CYA protects chlorine from rapid destruction by sunlight.

If your CYA level is too low, chlorine can disappear surprisingly quickly on a sunny summer day.

But more stabilizer isn’t always better.

2. Your Stabilizer (CYA) May Be Too High

CYA protects chlorine, but excessive CYA changes how much chlorine is needed to maintain effective sanitation.

This is particularly important for pools that use stabilized chlorine tablets because many common chlorine tablets add CYA every time they dissolve.

Over time, CYA can accumulate.

“My test says I have chlorine, so why am I still getting algae?”

The chlorine reading alone doesn’t tell the whole story. Chlorine and CYA need to be evaluated together.

This is one reason PFS Pool Services tests CYA as part of proper pool-water management rather than simply adding more chlorine whenever a pool has a problem.

3. Algae May Already Be Consuming the Chlorine

You don’t necessarily need to see a green pool to have an algae problem developing.

Chlorine is consumed as it oxidizes and sanitizes contaminants in the water. If algae is beginning to grow, chlorine demand can increase before the pool becomes visibly green.

• Chlorine disappearing unusually quickly
• Slightly cloudy or dull-looking water
• Slippery pool walls or steps
• Algae appearing in shaded areas
• Repeatedly needing more chlorine than usual

Adding more chlorine may temporarily raise the reading, but the underlying cause of the increased chlorine demand still needs to be identified.

4. Swimmers Are Increasing Chlorine Demand

Summer means more people using the pool—and every swimmer introduces contaminants into the water.

Sweat, body oils, sunscreen, cosmetics and other organic material all increase the work chlorine has to do.

A pool that maintained chlorine easily during a quiet week may behave very differently after a weekend pool party.

This is why chlorine requirements aren’t fixed throughout the year. Temperature, sunlight, swimmer load and water conditions all matter.

5. Hot Weather Can Increase the Problem

August in the South Bay can mean hot days, warm pool water and long hours of intense sunlight.

Those conditions can increase chlorine demand and make an existing chemistry or algae problem show up much faster.

A chlorine setting or dosing routine that worked earlier in the year may therefore need adjustment during peak summer conditions.

Saltwater pools aren’t exempt. A salt chlorine generator still has to produce enough chlorine to keep up with the pool’s actual chlorine demand. If chlorine production can’t keep up with chlorine loss, the free chlorine level will fall.

6. Your Circulation or Filtration May Be Part of the Problem

Water chemistry is only one part of maintaining a clear pool.

Your pump, filter and circulation system also need to move and filter the water effectively.

A chemistry problem can sometimes actually be a chemistry and circulation problem. That’s why simply adding another dose of chlorine isn’t always the best answer.

• Dirty filters
• Inadequate circulation
• Blocked baskets
• Incorrect pump schedules
• Poor circulation in certain areas of the pool
• Equipment that isn’t operating correctly

7. Something Else in the Water Is Creating Chlorine Demand

Leaves, pollen, dirt and other organic contaminants can all consume chlorine.

Phosphates can also contribute to conditions favorable to algae growth because phosphate is a nutrient algae can use. However, phosphate levels should be considered as part of the complete water-chemistry picture—not treated as the explanation for every chlorine problem.

The goal is to determine why the chlorine is disappearing before treating the pool.

Why Adding More Chlorine Isn’t Always the Answer

This is the most important takeaway:

If you’re continually adding chlorine, you need to find out why the pool isn’t holding chlorine.

The answer could be:

• Too little CYA
• Excessive CYA
• Developing algae
• Heavy swimmer load
• Organic contamination
• Circulation problems
• Filtration problems
• Increased summer chlorine demand
• Or a combination of several factors

Treating the wrong problem can mean spending more money on chemicals without actually solving anything.

Professional Pool Water Testing Matters

At PFS Pool Services, we don’t look at a chlorine reading in isolation.

Proper pool maintenance means looking at the overall condition of the water and equipment, including chlorine, pH, alkalinity, CYA and other important water parameters, along with circulation and filtration.

That allows us to determine what the pool actually needs rather than simply adding chemicals.

If your pool is consuming unusually large amounts of chlorine, repeatedly developing algae or simply won’t stay balanced, there is usually a reason.

PFS Pool Services can help identify it.

The Bottom Line

Your pool shouldn’t require you to blindly keep adding chlorine all summer.

Some increased chlorine demand is expected during hot, sunny weather and periods of heavy pool use. But if chlorine repeatedly disappears or the pool won’t stay clear, it’s time to look for the underlying cause.

Test the water. Check the equipment. Find the cause. Then treat the problem.

That’s a better approach than simply adding more chlorine.