Why Pool pH Keeps Rising (And How to Stop It)

Maintaining the right pH level in your pool is crucial for the health of your pool water, as well as the safety and comfort of swimmers. When the pH level in your pool rises above the ideal range (7.4 to 7.6), it can lead to several issues such as scaling, cloudy water, and reduced effectiveness of chlorine or other sanitizers. In this blog post, we will discuss why the pH in your pool may keep rising and what you can do to prevent it from becoming a problem.

What Is pH, and Why Is It Important in a Pool?

pH is a measure of how acidic or alkaline the water is. In pool water, pH levels are crucial for several reasons:

Sanitizer effectiveness: When pH levels are too high, chlorine and other sanitizers are less effective at killing harmful bacteria, algae, and other contaminants in the water.
Comfort: Water that is too alkaline (with a high pH) can cause skin and eye irritation for swimmers.
Equipment and surface protection: High pH levels can lead to scaling and mineral buildup on pool surfaces, pipes, and equipment, which can damage your pool over time.

Why Does Pool pH Keep Rising?

There are several factors that can contribute to a rising pH level in your pool. Understanding these causes can help you address the issue more effectively and prevent it from happening in the future.

1. High Alkalinity

One of the most common reasons for a rising pH level is high total alkalinity in the pool water.

Why this happens: Alkalinity acts as a buffer for pH, helping to keep it stable. However, when alkalinity is too high (above 120 ppm), it can cause the pH to rise, making it harder to maintain a balanced level.
How to fix it: Lowering the alkalinity will also help bring down the pH. To lower alkalinity, you can use muriatic acid or a pH decreaser. Test the water regularly to monitor both pH and alkalinity levels.

2. Adding Too Much Alkaline Chemicals

Using chemicals that increase the alkalinity of your pool, such as sodium bicarbonate (baking soda), can raise both pH and alkalinity.

Why this happens: Some pool owners may add alkalinity increasers to balance low alkalinity, but doing so can inadvertently cause the pH to rise above the recommended range.
How to fix it: Avoid adding too much alkalinity increaser. If you need to raise alkalinity, do so slowly and monitor both pH and alkalinity as you go.

3. Hard Water

Hard water, which contains a high level of calcium, can contribute to rising pH levels in pools.

Why this happens: Calcium hardness is related to pH. When calcium levels are too high, it can cause scaling on the pool’s surface, and the water may become more alkaline, raising the pH.
How to fix it: Test the calcium hardness level and aim for a range between 200 and 400 ppm. If calcium hardness is too high, you may need to dilute the water by draining and refilling the pool with fresh water.

4. Sunlight and UV Exposure

Exposure to sunlight and ultraviolet (UV) rays can cause the pH of your pool water to rise.

Why this happens: The sun’s UV rays can break down chlorine, which causes a chemical reaction that increases the pH level. UV exposure can also accelerate the evaporation of water, which can concentrate chemicals and make the pH rise.
How to fix it: Use a pool cover when the pool is not in use to reduce evaporation and protect the water from direct sunlight. Additionally, stabilizers like cyanuric acid can help prevent chlorine from degrading too quickly.

5. Aeration

Aeration is the process of introducing air into the water, which can also cause the pH to rise.

Why this happens: When water is aerated (for example, by waterfalls, fountains, or spa jets), carbon dioxide is released, causing the pH level to rise.
How to fix it: If your pool has fountains, waterfalls, or other aerating features, try reducing their use or adjusting the flow rate to minimize the aeration effect. If your pool’s pH continues to rise, check if any aeration features are creating too much turbulence.

How to Fix a Rising pH in Your Pool

Once you’ve identified the cause of the rising pH, it’s time to take action to bring it back to the ideal range. Here are some steps you can take to fix a high pH level in your pool:

1. Lower the pH with Muriatic Acid

Muriatic acid is commonly used to lower both pH and alkalinity in pools.

How to use it: Always follow the manufacturer’s instructions when using muriatic acid. You can slowly add the acid to the pool, preferably near the deep end, while the pump is running to help disperse the acid evenly.
When to add: Add muriatic acid in small increments and test the water after each addition to ensure the pH is coming down gradually. Avoid adding too much acid at once, as it can cause a rapid pH drop.

2. Use a pH Decreaser

A pH decreaser, also known as sodium bisulfate, is another option for lowering pH levels.

How to use it: Like muriatic acid, a pH decreaser should be added slowly to the pool water, and you should test the pH level after each addition to ensure it reaches the desired level.
When to use: Use pH decreasers if you want a more controlled, gradual reduction of pH compared to muriatic acid.

3. Monitor pH Regularly

Consistently testing the pH of your pool water helps you stay on top of any changes in the chemistry. It allows you to address any imbalances before they become major problems.

Test frequency: Test the pool water every 3-4 days if you are dealing with rising pH. If your pool is well-maintained, weekly testing should be enough.
Adjust chemicals as needed: Keep a record of the pH levels, and adjust chemicals according to the test results.

How to Prevent pH from Rising in the Future

Once you’ve brought your pH back to normal, it’s important to take steps to prevent it from rising again in the future.

1. Maintain Proper Alkalinity Levels

Keeping the alkalinity of your pool between 80 and 120 ppm helps to stabilize the pH and prevent fluctuations.

How to maintain it: Avoid over-adding alkalinity increasers, and test your pool’s alkalinity regularly. If it gets too high, you can lower it using muriatic acid.

2. Regularly Clean Your Pool

Keeping your pool clean helps maintain a balanced water chemistry.

How to clean: Skim the surface, vacuum the pool, and brush the walls regularly. Clean the filter and ensure that the pump is working efficiently.

3. Consider Using Stabilizer (Cyanuric Acid)

Cyanuric acid acts as a stabilizer for chlorine and can help prevent the sun’s UV rays from causing pH imbalances.

How to use: Add cyanuric acid to your pool if you’re experiencing rapid chlorine degradation from UV exposure. This can help keep your pool water more stable.

4. Avoid Over-Aerating the Pool

If your pool has fountains, waterfalls, or spa jets, avoid over-using these features, as aeration can raise the pH.

Reduce flow rates: Lowering the flow rate of aerating features will reduce the impact on pH levels.
Use aeration wisely: Only use aeration features when necessary, and monitor the pH levels carefully.

5. Regularly Test the Pool Water

Testing your water chemistry regularly is key to preventing pH from rising again. When pH, alkalinity, and calcium levels are balanced, it’s much easier to keep your water clear and healthy.

Test frequency: Regularly test your water, at least once a week during the swimming season, and adjust chemicals as needed to maintain the proper pH balance.