Does Chlorine Affect pH


Pool owners should remember that when super chlorinating or shocking your swimming pool, chlorine in a granular or liquid form can mess with pH levels at first but if you run a tight ship and have a well-balanced pool,  your pool’s water chemistry can handle any changes that come your way and any negative effects that come with using Chlorine. Does Chlorine Affect pH?

Sodium Hypochlorite or Bleach in liquid form, at 11-13 pH that may slightly change the pH of your pool that won’t last just as
Calcium Hypochlorite (“cal hypo”) in granular form when mixed with H2O, may cause an acidic pH change that is also temporary If Total Alkalinity (TA) is between 80-90 ppm.

 

Pool water starts with a strong chemical structure that will prevent negative happening or fast changes during those dog days of summer. Always remember TA or Total Alkalinity is the measurement of your pool water’s strong chemical structure. Without getting too technical, test and ward off any troubles before they happen.

 

Does Chlorine Raise or Lower pH

 

Pool owners all know or at least should know that Chlorine works the best at the right pH levels but sometimes when adding chlorine-like granular or shock chlorine the pH is affected by the chlorine itself as well as its total alkalinity. When alkalinity falls, it is more difficult to maintain a stable pH which can snowball and lead to problems.

Higher chlorine levels lower the pH of your pool’s water, making it more acidic dropping the levels below 7.0 pH. The more acidic the water, the higher the likelihood of corrosion. Corrosion can affect metal piping, equipment, and the surface of your pool tiles and concrete. It can also damage pool accessories ladders liners and anything else that goes into your swimming pool water

Normal pH range is considered anything between 7.2 and 7.6, 7.4 being ideal. But, it’s not always easy to keep it there. An occasional spike in the pH balance that may happen during super chlorinating your pool isn’t too much to be concerned about, but if you’re constantly battling keeping it in range after you shock your pool then you could have a bigger problem.

Shocking your pool is important, but if you’re using Cal-Hypo (Calcium Hypochlorite), is one of the various types of chlorine you can buy, and it looks exactly how you’d expect pool chlorine to look. It’s most commonly sold as a white, chlorine-smelling powder/granules, which are then poured directly into the pool water, or sometimes via the pool skimmer.

It can raise your pool’s pH levels temporarily. The main product is used in shocking your pool, but wait to do testing on all your chemistry balance levels consistently, especially after shocking. 

Allow the filtration system to circulate the chlorine or any dry chemical to mix and dissolve thoroughly throughout the pool water. It should be well-distributed within a few hours for better results. The best results are after a short time for ensuring a proper pH after the initial spike that normally will happen when you shock your pool.

 

Is Chlorine Acidic or Alkaline

 

Chlorine by itself is not acidic nor basic because it contains no H+ ions, but when it reacts with water (H2O) forming Hydrochloric and Hypochlorous acids it becomes an acid solution.

 When chlorine gas reacts with water it forms Hypochlorous acid and Hydrochloric acid, similar to how carbon dioxide reacts to form Carbonic acid. Hypochlorous Acid is ideal when used as a swimming pool disinfectant and sanitizer but creates some acidic properties to the mix. As a result, there is a net increase in the protons in the solution, lowering pH. In Chemistry it looks like this:

Hypochlorous Acid – is a weak acid with oxidizing properties formed when chlorine dissolves in cold water and used in bleaching and water treatment.

Hydrochloric Acid-Hydrochloric acid (HCl) is a strong acid. Its pH can be as acidic as low as pH 0.0

So when chlorine shock either powder or granular is added to the water (H2O) in your pool their reaction with water makes forms of acid that can lower the pH in the water’s balance.

Does Liquid Chlorine Raise pH?

 

Liquid chlorine and bleach which is called Sodium hypochlorite or Bleach have a pH of 11.0 to nearly 13.0 so it is logical to think that they will raise the pH of the pool water. The fact is that initially or upon addition liquid chlorine raises pH because sodium hydroxide (lye) is made which is on the base side of the pH scale.

Here is what happens when liquid chlorine sodium hypochlorite – NaOCl is added to pool water:

NaOCl + H2O → HOCl + Na+  + OH

Sodium hypochlorite and water form Hypochlorous acid and Sodium-ion and Hydroxide ion. Remember that hypochlorous acid is HOCl is the killing form of chlorine is made, sodium ions (Na+) and hydroxide (OH–) are made. The hydroxide raises the pH of the pool water. Liquid chlorine raises the pH of pool water.

 

As the liquid chlorine or Sodium Hypochlorite is consumed in the pool that small expected spike is reduced with sunlight (UV Light) and agitation to nothing in a normal size pool, as long as the Total Alkalinity is stable then this is the strength of balance that will keep low or high spikes from having an effect on the pH of your swimming pool.

This is another reason that pool water is so dependent on Total Alkalinity. Most large pool owners agree to keep a well-balanced pool TA (Total Alkalinity) needs to be in a solid 90-100 ppm range Start with a Target TA of 90 ppm and adjust up or down in 10 ppm increments until pH remains stable depending on whether the pH is drifting up or down.

Cyanuric acid technically is an ‘acid’ but is dissimilar to muriatic acid, which the pool industry uses to manage and adjust pool pH levels. It is sold as a standalone product or can be purchased as a convenient additive to chlorine tablets. It is able to dissolve in water and has a little overall effect on pH, alkalinity, or hardness.

Organic chlorine is Trichlorisocyanuric Acid and Dichlorisocyanuric Acid dissolves rapidly and is suitable for small pools along with Inorganic chlorine is Calcium Hypochlorite for daily and shock chlorination and Sodium Hypochlorite in liquid form all have a very small effect on a swimming pool’s pH level on a well-balanced pool.

Start your pool with a target TA (Total Alkalinity) of 90 ppm and adjust up or down in 10 ppm increments until pH remains stable depending on whether the pH is drifting up or down and help keep these controls these other pool water conditions.

 

Free chlorine:
Combined chlorine:
Total chlorine:
Cyanuric acid:
Salinity:
0,5-1,6 ppm (mg/l)
0-0,4 ppm (mg/l)
Max 2,0 ppm (mg/l)
30-50 ppm (mg/l)
Max 250 ppm (mg/l) (0,025%)

 

MyWaterEarth recommends keeping a schedule for testing your pool’s water. Check this  LaMotte Test Kit available through Amazon & get one for the summer  LaMotte ColorQ Pro 9 Plus Digital Liquid Pool & Spa Chemical Water Testing Kit

Keeping the (TA) Total Alkalinity 80-100 ppm in your pool a constant-strong proper range will keep your swimming pool’s water in a direct course for well-balanced chemistry that can tackle the issues before they become problems that will surely come with heat and usage in the coming summer months.

 

 

      JimGalloway Author/Editor

 

 

 

References:   pH and Chlorine values for good water quality

The Chlorine Institute-Sodium Hypochlorite 

 

 

 

 

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