Calcium Hypochlorite ph, Alkalinity & Hardness: A Quick Guide!

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Calcium Hypochlorite is very popular as a pool shock as it has very high active chlorine content (65% – 70%) and no cyanuric acid (CYA). However, it has a few disadvantages.  Calcium Hypochlorite has an adverse effect on pH, total alkalinity and calcium hardness of the pool water.

What Does Calcium Hypochlorite Do to pH?

Calcium hypochlorite (aka Cal Hypo) will raise the pH levels of your pool slightly. Cal Hypo, when dissolved in water, forms Hypochlorous acid and Calcium Hydroxide. Hypochlorous acid is a disinfectant and gets used up in neutralizing the contaminants. Calcium Hydroxide, on the other hand, is a base and increases the pH of your pool.

The increase in pH after each shock is small but you may see the pool pH go up over time. However, you must test the pool water and bring down the pH level within the 7.2 – 7.8 range. This can be done by adding the correct amount of muriatic acid to the pool water.

Calcium Hypochlorite pH, Total Alkalinity and Calcium Hardness

Cal Hypo is a powerful & effective oxidizer & sanitizer used to kill bacteria, algae, and other contaminants, real fast. Calcium hypochlorite works by releasing chlorine into the water, which oxidizes and destroys organic matter in the pool.

I recommend the use of cal hypo for shocking your pool on a weekly basis, but you must always readjust the pH to within the safe range of 7.2 – 7.8. High pH levels reduce the effectiveness of chlorine as a pool sanitizer. The result will be skin and eye irritation for swimmers. It can also cause scaling on pool walls and cloudy water.

How Does Calcium Hypochlorite Affect Alkalinity?

Calcium hypochlorite increases the alkalinity of the pool significantly because it forms calcium hydroxide, in addition to hypochlorous acid. Total alkalinity is a measure of the amount of dissolved alkalis, which includes calcium hydroxide, in your pool.

NOTE: Quite often it is assumed that pool alkalinity and pool pH mean the same thing. In fact they are different, even though they are closely related.

Total alkalinity is measured in ppm, whereas pH is measured on a scale from 0 to 14.

High alkalinity levels in your pool make it quite difficult to control and manage pH swings. An increase in total alkalinity level increases the ability of your pool water to resist changes in pH.

It is therefore very important to check the total alkalinity level of pool water after using cal hypo shock. If the total alkalinity is higher than 150 ppm it should be lowered. The ideal range for total alkalinity in a pool is between 80 and 120 ppm.

High total alkalinity will result in scaling, cloudy water, reduced chlorine effectiveness and unstable pH levels. Use a pool test kit to measure the total alkalinity level. If it is above 120 ppm lower it by adding muriatic acid or sodium bisulfate.

Does Cal Hypo Raise Calcium Hardness?

Cal Hypo does indeed raise calcium hardness levels in swimming pools. Calcium hardness increases because of the addition of Calcium Hydroxide from Cal Hypo. High calcium hardness will result in calcium deposits on pool plumbing and walls.

Calcium hardness is a critical parameter in pool water chemistry, as it measures the amount of dissolved calcium ions in the water. The ideal range for calcium hardness is 200 – 300 but in any case it should be kept below 400. 

Water with high calcium hardness is also referred to as hard water. 

Calcium hardness exceeding 400 will result in calcium deposits on pool plumbing, pumps and filters leading to corrosion and reduced lifespan. It will also cause scaling of pool walls & bottom making them rough. A rough pool is more likely to promote algae growth.

High calcium hardness will also cause the pool water to be cloudy.

Bottom Line

Using Cal Hypo as a pool shock is highly recommended as it has a very high %age of chlorine and will not increase the cyanuric acid levels of your pool. However, Calcium Hypochlorite will increase the pH, total alkalinity and calcium hardness.

Test your pool chemistry after shocking it and ensure that all critical measurements are restored to ideal levels as per infographic below:

Recommended Levels for Pool Chemistry

If this the first time you have got a pool in your backyard, I highly recommend checking out my blog post Pool Chemistry for Beginners: With 5 Super Helpful Cheat Sheets!

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

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