What Chemicals Do: Total Alkalinity and Calcium Hardness

Our third installment of important pool chemicals focuses on the two main supporting chemicals that are necessary for every pool operation. They aren’t the two main stars, like chlorine and pH, but nevertheless they play an important role in keeping your pool water clean and safe!

So let’s get started with this pair!

What is Alkalinity?

Total Alkalinity, not to be confused with something alkaline which is basic on the pH scale, is an important measure separate from pH, but it does have an effect on pH.

Sophisticated science aside, it contributes to the stability of pH in your pool.

What is Calcium Hardness?

Calcium hardness is the amount of dissolved calcium in the water. You may be wondering, “Wait, how is calcium getting into my pool?!” That is a valid question, and one that’s easily explained!

One explanation is that all water, even drinking water, contains calcium; not in large amounts, obviously, but it does. Hard water at home means that it has higher amounts of dissolved calcium in the water, whereas soft water has low to no calcium.

The primary way we get larger amounts of dissolved calcium in our pools is from our chlorine. Remember how our recommended form of adding chlorine was by using calcium hypochlorite? Well, obviously when we dissolve and add that to your pool, it adds chlorine, but it also adds the calcium used to bind the chlorine!

Why adjust Alkalinity?

So we know that alkalinity affects the stability of pH in our pools. But that doesn’t mean we need to adjust alkalinity, right? Actually it does. Remember in our pH post how we talked about how people coming into your pool can change your pH, and if it’s too high it makes your chlorine ineffective? Well then, it would seem it’s important to keep our pH in check.

But if we have low total alkalinity in our pools, the pH will bounce around wildly, even with minimal factors influencing it. What this leads to though is a wasteful usage of chemicals. If we add acid to get our pH down, and it’s extremely effective, that’s great. Until, that is, we realize that what we added was too effective, and now we need to raise pH. And the cycle then continues, bouncing back and forth above and below the desired range. Not to mention if we add people to that equation!

So having a total alkalinity that serves to anchor down your pH, and keep it from fluctuating wildly at every whisper of change can save you a lot of chemicals and money!

Why adjust Calcium Hardness?

Calcium hardness is important to have in your pool water at all times for one very simple reason. Water is hungry, and water that doesn’t have the calcium it desires will try to leach it out of anything it comes into contact with. Whether it’s getting it from your pool shell, your paint, your piping, or even the inner workings of your pumps!

The result of this would be brittle and breaking pool equipment and surfaces! But luckily it’s an easy fix!

What chemicals adjust Alkalinity and Calcium Hardness?

For these two chemical readings there are two chemicals that we use to adjust them, and ensure your pool keeps running smooth and efficiently!

Alkalinity utilizes sodium bicarbonate. Now you may be saying, “wait a second, I use that at home!” And you’re correct, sodium bicarbonate is baking soda, however I would NOT recommend using the industrial strength stuff we use in the pools to bake with at home. Alkalinity will naturally dissipate, and adding muriatic acid lowers pH naturally.

Calcium Hardness is raised by use of the chemical calcium chloride. Which may also sound familiar as it is a chemical that is commonly used to melt ice and keep walkways clear in winter! There is no way to lower calcium hardness other than expensive chemicals that are unnecessary, or by replacing portions (or all) of your pool water with fresh water.

How dangerous are the chemicals?

While sodium bicarbonate is certainly not going to hurt you if it comes into contact with your skin, precautions should still be used. Minimally, using a respirator, and eye protection will keep you safe.

Calcium chloride on the other hand, when mixed with water, has an exothermic reaction, which is to say, it gets hot! So make sure you use a respirator, eye protection, and definitely wear gloves to keep your hands safe!

Alkalinity and Calcium Hardness in Daily Operations

Alkalinity and calcium hardness don’t fluctuate nearly as much as pH or chlorine so monitoring them only needs to be done once a day, and can be checked using a titration kit, or a photometer.

A good way to track your alkalinity and calcium hardness levels over time, is using the Chemical Records Module in DigiQuatics.

Optimal range for alkalinity is roughly between 60-120 ppm. Just remember, the higher you go, the harder time you will have affecting change on your pH, in either direction.

Calcium hardness should be kept at 250 ppm minimum. Once full, getting your pool to 250 ppm is important; from there if you’re using calcium hypochlorite to add chlorine to your pool your calcium hardness will steadily increase. There is no real reason to lower your hardness. At several of the facilities I’ve worked for, before we drained and refilled the pool (annually) the calcium hardness could get up to 2300 ppm without issue!

Further information on Alkalinity, Calcium Hardness, and other pool chemicals can be found here.

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Have any questions or experience with these chemicals? Let us know below! We’re happy to answer questions!

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