Does Chlorine Raise or Lower pH?

Diving into the world of pool maintenance can make you feel like a real mad scientist when you’re first starting out. You know you need a plethora of test strips to routinely check the levels of various chemicals in your pool to ensure the safety of your pool and swimmers. But what does each chemical do, and how does it impact your pool?

For this article, we are going to focus on chlorine. Chlorine is a chemical commonly used to sanitize pool water. Putting chlorine in your pool removes viruses, bacteria, and other waste and debris, making it safer for swimmers. It can be purchased in liquid, tablet, or powder form.

How does chlorine impact your pool’s pH levels? pH is a quantitative measure of the acidity or basicity of your pool water. Higher pH can result in skin irritation and dryness. Lower pH levels can sting swimmers’ eyes. 
Does chlorine raise or lower your pool’s pH levels? That depends. Liquid chlorine typically has a pH level of thirteen, which causes a raise in pH in your pool. However, when the added chlorine is consumed over time, this is an acidic process and the pH drops back down close to where it started. So, you will see a spike in pH when you first introduce your chlorine into your pool, but through circulation and with time, those levels will drop back down.

Key Terms for Pool Maintenance

Before we continue on, let’s define a few important terms you’ll run into when researching pool maintenance:

• Cyanuric acid: Also called “CYA,” this is a chlorine stabilizer for swimming pools. CYA forms a weak bond with free chlorine in the pool water, which protects the chlorine from UV rays that reduce chlorine levels.
• Free chlorine: This is essentially the chlorine you test for in your pool’s water, it’s the chlorine that is available to sanitize your pool. You will also see this referred to as “FC.”
• Combined chlorine: This is chlorine that has already been used up by the sanitation process of water.
• Alkalinity: This is the volume of water that fights against acidification. Simply put, it’s a measurement of your pool’s ability to neutralize acids and bases while maintaining a pH level that allows for precise water quality.

How Much Chlorine Your Pool Really Needs

Generally speaking, residential pools should have an FC level of around 7.5% of the CYA minimum (this level needs to be no more than fifty parts per million [PPM]). Remember that CYA stabilizes FC, protecting both the chlorine from the sun but also protecting your swimmers from the harsh effects of concentrated chlorine. The Environmental Protection Agency (EPA) and Center for Disease Control (CDC) claim the maximum FC that is safe for swimmers is four PPM. 

7.5% of fifty PPM CYA is 3.75 PPM of FC, which is below that maximum level. For example, say you have an FC of ten PPM. But isn’t ten PPM above the recommended level? Yes, but we haven’t factored in the CYA levels. 

CYA in your pool water lowers the exposure of FC. So, in this example, even if you have ten PPM of FC, the CYA in the water makes it so that the exposure is only 3% to 7% of the ten PPM. This means your overall FC level will range from 0.3 to 0.7 PPM of FC. Without the CYA, your swimmers would be exposed to all ten of the PPM.

What Is the Correct Total Alkalinity and pH?

Your total alkalinity works with your CYA to create buffers in the pool water, preventing the pH from changing too quickly. Total alkalinity typically causes the pH of water to increase, so if you have higher alkalinity (over 100 PPM), it will raise the pH. To lower this, you will need to frequently add acid to lower the pH.

Generally speaking, ninety PPM is the ideal alkalinity for residential pools. The ideal target for pH levels is exactly 7.5. Many websites will cite a range to maintain your pH level in, but when you shoot for a range, you may miss certain problems that arise when your pH levels are under or above 7.5. If you need to know how to raise pH in your pool naturally, we recommend checking out our other posts for more information.

In Closing

Chlorine generally increases the pH in your pool, but with time, aeration, and CYA, these levels can be stabilized and safe for swimming. CYA balances out the harmful effects of chlorine while protecting both it and your swimmers. To get the most out of your pool, maintain a pH level of 7.5!