Chlorine is the most popular sanitizer used in pools today. And for good reason. It’s effective and works well. But does it impact your pool’s pH levels? Or does that only happen when you use too much? And does it apply to all types of chlorine as well as saltwater pools?
Does Adding Chlorine Raise or Lower pH?
The truth is, that large amounts of some chlorine types, namely Trichlor, can significantly lower your pool’s pH level. When chlorine (CI2) is added to a pool, some of the chlorine reacts with the water (H2O) to produce hypochlorous (HOCl) and hydrochloric acids (HCI). As more of these acids are produced, the water pH is gradually lowered.
Cl2 + HOH → HOCl + HCl
There are also some chlorine types that increase your pool’s pH level.
That being said, things get a bit more complicated when you consider all the different chlorination methods and products out there. But before we get into those, it’s important to understand the balance between acidity and chlorine.
What are the Ideal Levels of Chlorine and pH?
As you probably know, the purpose of chlorine is to sanitize the water from bacteria and pathogens. But most people don’t realize that the effectiveness of chlorine as a disinfectant is directly related to water acidity.
In fact, Cl2 is most effective in water with a pH of 5-6. As you raise the pH, you are also decreasing the disinfecting power of the chlorine. Here is a rough estimate of how steep the decline really is:
|Acidity Level (pH)
But as you probably know, the ideal pH level for a pool is 7.4 to 7.6. Before you get discouraged, consider the fact that sanitizing pool water with Cl2 doesn’t require more than 50% effectiveness. So, as long as you keep the pH in the optimal range, your pool will be thoroughly sanitized.
pH of Different Pool Chlorine
Here’s a summary of the pH level of different types of chlorine. As you can see, the pH varies considerably depending on the chlorine type.
|Liquid chlorine (sodium hypochlorite)
|Depending on the type: 3 to 13
|Calcium hypochlorite (cal-hypo)
|Saltwater chlorine generator
The pH of liquid pool bleach measures at 11-13, depending on the product. After it is initially added, the pool water becomes less acidic (higher pH). But as liquid chlorine degrades, it generates considerable amounts of hydrochloric acid (HCl), which eventually brings the pH back down.
Because liquid chlorine products are not stabilized, sunlight can significantly accelerate the degradation process. This, in turn, will lower the pH even faster. So unless you want to constantly add chlorine to your water, add a Cl2 stabilizer.
Chlorine stabilizer is called Cyanuric Acid or CYA for short. It should be maintained at 30-50 ppm in a pool. If the water already has CYA in it, you will not need to add more. The only way you can remove it is by removing water, either through draining or splashing.
Chlorine tablets affect the pH much like the liquid version. However, while liquid bleach has a pH ranging from 11 to 13, the pH of different tablets spans from as low as 3 (trichlor) and as high as 12 (cal-hypo). Plus, there are many more variations of solid-state Cl2 products than the liquid kind. Follow along for a close look at each one.
There’s a reason it’s safe to add Dichlor to a pool even when it’s occupied. In fact, this is the only go-to product for spas. And it’s all because Dichlor tablets are stable and have a neutral pH of ~7, which means they won’t cause any initial change in pool acidity. However, since it is still a form of chlorine, it will slightly lower the pH over time.
We recommend adding Borax to balance out the acidity in pool water treated with Dichlor. Keep borax levels at around 35 ppm.
Unlike its neutral cousin Dichlor, Trichlor is highly acidic. It measures a pH of 2.5-3 and contains a stabilizer (cyanuric acid). Trichlor comes in tablet form and also granular form.
As such, overuse of trichlor will lower your pool’s pH level making the water acidic. It will also raise stabilizer levels if it’s the only chlorine product used.
Trichlor is only recommended for pools with very high pH and alkalinity levels.
That said, countering Trichlor’s acidity is as simple as adding a bit of soda ash into your pool.
Saltwater pools suffer from creeping pH. That is, chlorine generators actually raise the pH of your pool. Luckily a simple pH Down or muriatic acid solution can effectively even out the acidity.
Calcium Hypochlorite is another form of granular chlorine with a neutral pH. However, when it’s mixed with water, Cal Hypo reacts, losing acidity until it settles in the 10.5-11 pH range. As you can guess, this raises the pH of your pool very slightly. There is barely any risk of going over the recommended (7.4-7.6) pH level unless cal-hypo is the only sanitizer type you use.
If you have an indoor pool, Cal Hypo is probably your best option. Unfortunately, it’s not a stabilized chlorine product, so it will quickly degrade in the sun. To remedy this problem, make sure the water has cyanuric acid present. If it doesn’t, you can add some, with ideal levels being 30-50 ppm.
Instead of adding Cl2 directly, saltwater pools are chlorinated via chlorine generators. You simply add granular salt to the pool water and the generator slowly transforms the salt water into chlorine. At the same time, the generator also produces a byproduct called sodium hydroxide, which has a pH of 13.
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