Does Chlorine Raise or Lower pH? (What’s the Best Balance?)

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Does Chlorine Raise or Lower pH?

Of course, you want to make sure your pool is always ready for a refreshing dip. Adding chlorine is essential to keeping your pool sanitized & safe for swimming. But chlorine alters the pool chemistry in more ways than one. It’s easy to get confused about the  effect chlorine will have on the pH level. Does Chlorine Raise or Lower pH?

The reason for the confusion is because different chlorine types have different effects on pool water pH.

  1. Liquid Chlorine (Sodium Hypochlorite) may lower the pH level marginally. 
  2. Cal Hypo (Calcium Hypochlorite), a granular shock, will raise the pH as a result of increase in calcium levels in your pool.
  3. Trichlor, used for regular pool sanitization, will lower the pH level as it contains Cyanuric Acid (CYA). CYA is not only acidic but is also a pH buffer. 
  4. Dichlor, also a granular shock, may lower the pH level, but only marginally.
Does Chlorine Raise or Lower pH?

The Effect of Liquid Chlorine on Pool pH

When Liquid Chlorine (Sodium Hypochlorite) is added to the pool, it tends to marginally lower the pH level of the water. Liquid chlorine (Sodium Hypochlorite) is, in fact, highly alkaline as it has a pH of 13. So why does it marginally lower the pool pH?

When liquid chlorine is added to pool water, it reacts to form hypochlorous acid (HOCl) and sodium hydroxide (NaOH). Sodium hydroxide is a basic substance and should raise the pH level. 

However, hypochlorous acid, which is mildly acidic, gets converted to hydrochloric acid (HCL) which is quite acidic. The conversion is a result of photodegradation of free chlorine (FC) as well as the formation of combined chlorine (mostly chloramines).

The higher acidity of the hydrochloric acid more than neutralizes the basicity of sodium hydroxide. The net result is that the pH of your pool may drop marginally.

The Effect of Cal Hypo Shock on Pool pH

Granular Cal Hypo (Calcium Hypochlorite) shock will raise the pH level of your pool. Cal Hypo, after all, is a compound of calcium and has a pH of 11.8. Naturally it contains a significant amount of calcium, which is an alkaline substance. 

When Cal Hypo (Calcium Hypochlorite) is added to the water, it breaks down into hypochlorous acid (HOCl) and calcium hydroxide (Ca(OH)2). The calcium hydroxide, being an alkaline substance, increases the pH level of the water.

You will find that pH, Total Alkalinity (TA) and Calcium Hardness (CH), all go up, after shocking your pool with granular Cal Hypo.

The Effect of Trichlor on Pool pH

Trichlor is the most popular source of chlorine for sanitizing an outdoor pool. It comes in 1” or 3” tablets that can be inserted in floaters or in the skimmers. It dissolves slowly and you can set it up in a way that it needs to be refilled only once a week.

Trichlor has cyanuric acid (CYA) built into the formulation so the free chlorine is already stabilized and will be able to withstand the destructive effect of the sun’s UV rays.

However, Trichlor has a very low pH of just 2.8. Moreover, the CYA in it is both acidic and a pH buffer. The net result is that Trichlor lowers the pH level of your pool significantly.

The Effect of Dichlor Shock on Pool pH

Dichlor is a granular form of chlorine and is sometimes used to shock or super chlorinate a swimming pool, especially if the cyanuric acid (CYA) levels are low. 

Dichlor is stabilized chlorine (contains CYA stabilizer) and is pH neutral. The pH of Dichlor is typically between 6.5 and 7.0. Dichlor has a minimal impact on the pH of the pool.

Dichlor will react with water to form hypochlorous acid and ultimately hydrochloric acid. The net effect is a very slight drop in pool pH, after using Dichlor shock.

Adjusting pH Changes Resulting from Chlorine

So chlorine certainly can have an effect on the pH level. Whether pool pH will go up depends on the type of chlorine used. However, you can not use chlorine as a substitute for a pH increaser or decreaser.

The pH level should be tested regularly and adjusted as needed to maintain a safe and comfortable swimming environment.

If the pH level is too high, pH decreaser (sodium bisulfate) can be added to lower it, and if pH is too low, pH increaser (sodium carbonate) can be added to raise it.

What Is the Ideal pH Level for Chlorine?

The ideal pH level for chlorine in a swimming pool is between 7.2 and 7.8. This range is recommended by the Center for Disease Control (CDC) and the National Swimming Pool Foundation (NSPF) for several reasons.

Chlorine Effectiveness and pH

The effectiveness of pool chlorine, as a sanitizer, is optimized when pH level is maintained  between 7.2 and 7.8. 

At a pH level of 7.5, approximately 80% of the chlorine in the water is in the active form of hypochlorous acid. Hypochlorous acid is the component that kills bacteria, viruses and algae.

Safe Swimming Conditions

A pH level between 7.2 and 7.8 is safe for humans. Swimmers will experience burning eyes and dry skin if the pH is too low. On the other hand they will experience skin and eye irritation if the pH is too high. The water may also be cloudy. Low visibility creates unsafe swimming conditions.

Reduced Pool & Equipment Lifespan

The lifespan of the pool and its equipment is the longest when pH is maintained between 7.2 and 7.8.

When the pH level is too low, the water becomes acidic, which can corrode metal equipment and cause damage to the pool’s plaster or vinyl liner. 

Conversely, when the pH level is too high, the water becomes alkaline. The result is scaling on the pool’s surfaces and equipment.

Thank you very much for reading the post. I do hope you found it informative and helpful.

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