Perfect Pool Chemistry: How to Choose the Right Chlorinator Size for Crystal-Clear Water!

Why Do Chlorine Levels Drop to Nearly Zero in Summer? Let’s Find Out

Maintaining proper chlorine levels in your pool during the scorching summer months can be a real challenge. There are several reasons why your chlorine levels may drop to almost zero, and understanding these factors is crucial to keeping your pool clean and safe. Below, we’ll explore the most common causes. While all are important, the last point could be the root cause of all your troubles, so we’ll dive into it in greater detail.

1. Low Salt Levels

Salt chlorinators are designed to function within a specific salinity range. If the salt concentration in your pool water falls below the required level, the chlorinator will struggle to produce enough chlorine—or it may stop producing chlorine altogether. Regularly testing and maintaining your pool’s salt levels is key to ensuring proper chlorine generation.

2. Faulty Chlorinator

A faulty chlorinator is an obvious cause of low chlorine, but it can sometimes be tricky to diagnose. The simplest way to check is to observe the chlorinator cell during operation. If you see a whitish cloud inside the cell, that’s a good indication that chlorine is being produced. If no cloud is visible, the chlorinator may need repair or replacement.

3. Dirty Chlorinator Cell

Over time, your chlorinator cell can become coated with deposits, affecting its ability to produce chlorine. During the chlorination process, the salt in your pool water is broken down into chlorine gas, hydrogen gas, and sodium hydroxide (NaOH). Sodium hydroxide, also known as lye or caustic soda, is a white, odorless, and corrosive solid. It does not build up on the cell plates and water flow sensor , this is more commonly calcium build up.

When this happens, the chlorinator becomes less effective, and chlorine production decreases. To fix this, clean the cell by soaking it in a weak hydrochloric acid solution (approximately 10%). This will remove the buildup and restore the cell’s functionality.

4. Bacteria and Pathogens

Chlorine’s primary role is to sanitize your pool by killing bacteria and pathogens. If chlorine levels are consistently low, bacteria can thrive, making it difficult to maintain water quality. Addressing other factors (like salt levels and cell maintenance) will help ensure your pool has sufficient chlorine to combat these contaminants effectively.

5. Incorrectly Balanced Water

Water balance plays a critical role in chlorine efficiency. If your pool water is not properly balanced, it will struggle to make effective use of the chlorine.

One of the biggest culprits in summer is the sun. The sun’s ultraviolet (UV) rays break down chlorine through a process called chlorine degradation. In just two hours, up to 90% of your pool’s chlorine can evaporate into the atmosphere.

To combat this, you’ll need to add a pool stabilizer, also known as cyanuric acid. Cyanuric acid acts as a sunscreen for your pool, protecting chlorine from being destroyed by UV rays. Maintaining the correct cyanuric acid levels ensures your pool retains chlorine longer, even under intense sunlight.

6. Incorrect cell size

To correctly understand chlorine production in pools one need to understand how the chlorinator is producing chlorine. The chlorinator is simply a power supply producing current flow through the electro plates of a cell. The cell plates of a chlorinator are usually made of titanium and coated with ruthenium and sometimes iridium: 

• Titanium: A corrosion-resistant material that is commonly used for the plates. 

·         Ruthenium and iridium: A coating that is applied to the titanium plates. The ruthenium oxide in the coating is sacrificed during the electrolysis process to produce chlorine. The composition of the coating affects the cell's efficiency and lifespan. 

Explains why chlorinator cells are so expensive. Older models of chlorinators used perforated or mesh plates instead of solid plates.

One of the first questions to consider is how much chlorine is required to maintain your pool within the recommended levels of 2–4 PPM (parts per million). This range ensures your pool stays clean and safe for swimming while avoiding over-chlorination.

It’s also important to keep in mind that chlorinator cells degrade over time. The more you demand from your chlorinator (e.g., running it at 90–100% output consistently), the faster the cell plates will deplete, shortening their lifespan. Running your chlorinator at 50% of its maximum output not only extends the lifespan of the cell but also reduces maintenance and replacement costs in the long run.

Let’s answer the key question: How do you calculate the correct chlorinator size for your pool to maintain 3 PPM chlorine?

To calculate how much chlorine a chlorinator needs to produce to maintain 3 ppm (parts per million) of chlorine in your pool, you must first understand the relationship between your pool’s volume, chlorine demand, and your chlorinator’s production rate.

Understand What PPM Means

• PPM (parts per million) is a unit of concentration that indicates how much chlorine is in the water.
• For pools, 3 ppm means 3 milligrams of chlorine per liter of water.

Calculate How Much Chlorine You Need

To increase chlorine levels to 3 ppm, calculate how many milligrams (mg) of chlorine you need for the pool’s total volume.

1. Formula:
   Chlorine Needed (mg) = Volume (liters) × Desired PPM
2. Example Calculation:
   For a pool with 75,000 liters of water:
   Chlorine Needed = 75,000 × 3 = 225,000 mg = 225 g

This means you need 225 grams of chlorine to achieve 3 ppm in your pool.

Understand Your Chlorinator’s Output

A chlorinator produces chlorine by converting salt in the water into chlorine gas. Chlorinator output is typically measured in grams of chlorine per hour (g/hr).

1. Check your chlorinator's specifications to determine its production rate. For example:

• A chlorinator might produce 20 g/hr of chlorine under ideal conditions.

Divide the chlorine needed by the chlorinator’s output to find the runtime required.

Formula:
Runtime (hours) = Chlorine Needed (g) ÷ Chlorinator Output (g/hr)

3. Example Calculation:
   If the pool needs 225 g of chlorine and the chlorinator produces 20 g/hr:
   Runtime = 225 ÷ 20 = 11.25 hours

This means the chlorinator must run for approximately 11.25 hours to produce enough chlorine to maintain 3 ppm.

Account for Daily Chlorine Loss

Chlorine is lost daily due to factors like sunlight, pool usage, and contamination. On average:

• 50% of chlorine can be lost daily to sunlight if no stabilizer (cyanuric acid) is used.
• The actual chlorine demand depends on your pool's condition, bather load, and weather.

If your pool loses 2 ppm per day:

• Chlorine required to replenish = Volume × Loss in PPM
• For a 75,000-liter pool: 75,000 × 2 = 150,000 mg = 150 g

Your chlorinator needs to produce at least 150 g of chlorine daily to maintain 3 ppm.

Why a 20g/hour Chlorinator is Too Small for Your Pool

Let’s take a closer look at the reality of running a 20g/hour chlorinator for a pool that requires 150g of chlorine per day. It quickly becomes evident that this chlorinator is undersized, and here’s why:

Problem 1: Limited Runtime

Most pool owners run their pump for an average of 8 hours per day because that’s the common advice they’ve received. However, this advice is often given without considering calculations or the specific needs of their pool.

Using the calculation above:

• A 20g/hour chlorinator running for 8 hours produces:
  20 g/hour × 8 hours = 160 g

At first glance, this seems sufficient to cover the daily chlorine demand of 150g. However, this assumes:

1. The chlorinator runs at 100% output all the time.
2. Chlorine loss due to heat, sunlight, and contaminants doesn’t increase unexpectedly.

If the pool has increased chlorine demand during hotter days, higher bather loads, or when debris accumulates, the pool could quickly fall behind on chlorine levels.

Problem 2: Faster Cell Wear

Running the chlorinator at 100% output every day significantly shortens the lifespan of the cell plates. Chlorinator cells are designed to last a specific number of operating hours, but at full power, their longevity decreases drastically.

For example, if a cell has an expected lifespan of 10,000 hours, running it at 100% output:

• 10,000 ÷ 8 hours/day = 1,250 days = ~3.4 years

However, running the chlorinator harder to keep up with chlorine demand will lead to faster depletion, potentially reducing the cell lifespan by a year or more.

Solution: Use a Larger Chlorinator

The best approach is to oversize the chlorinator so it can meet the pool’s chlorine needs without running at full capacity. Ideally, the chlorinator should only operate at 50% output to preserve the cell lifespan while maintaining chlorine levels.

1. Calculate Required Output at 50%:
   If the pool needs 150g of chlorine per day, the chlorinator should produce that amount over 8 hours at 50% output.

Formula:
Required Output = Chlorine Needed ÷ Runtime ÷ Output Percentage

Example:
150g ÷ 8 hours ÷ 0.5 = 37.5 g/hour

This means the chlorinator needs to produce 37.5g/hour at 100% capacity to meet the pool’s chlorine demand with only 50% power usage.

2. Select a Chlorinator with Higher Output:
   A chlorinator rated at 40g/hour or higher would be ideal for this scenario. At 50% power, it can easily maintain the pool’s chlorine levels while preserving the cell's lifespan.

Economic and Practical Benefits

• Lower Operating Costs: By running the chlorinator at 50%, you reduce wear and tear, avoiding the need for frequent cell replacements, which can cost hundreds of dollars.
• Longer Cell Lifespan: Cells last longer when they don’t operate at full power constantly.
• Better Chlorine Stability: A larger unit can easily meet the demand during peak summer months when chlorine loss is higher due to UV rays and warmer water temperatures.
• Fewer Headaches: Oversizing the chlorinator ensures that you won’t have to constantly monitor and adjust chlorine levels, saving you time and effort.

Conclusion

Choosing a properly sized chlorinator from the start can save pool owners from frustration and extra expenses. A 20g/hour chlorinator might seem sufficient on paper but quickly falls short in real-world conditions, especially in larger pools or during summer. By investing in a chlorinator that can produce at least 37.5g/hour, you’ll ensure your pool remains clean, safe, and easy to maintain without the need for excessive runtime or frequent equipment replacements.

This decision may cost more upfront, but it will pay off in the long run with lower maintenance costs, better water quality, and fewer headaches!

If you have issues with your pool or chlorinator please contact us or leave a comment. Thanks for reading!