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How to add calcium to a swimming pool the right way

November 20, 2017

My name is Greg Beard, and I have been in the pool service business for many years. One of the questions I often get from service techs is how to add calcium the right way. It's not as simple as it don't just throw it in the pool. Calcium doesn't dissolve the same way as dry acid or shock.

Why add calcium?

Until recently, I underestimated how important calcium hardness is for water chemistry. Good calcium hardness levels make managing pool chemistry so much easier! As a service tech, my route is less stressful as a result of having LSI balanced water.  I test for calcium once a month, and add calcium to my pools that need it. My job has been so much easier ever since. The water behaves in a more predictable way, and I know I'm doing what's best for my customers.

I live in Orange County, California, and our weather is pretty awesome, most of the year. But that doesn't mean it never gets colder in the winter. Water temperature getting colder seriously affects the balance and makes for more corrosive pool water. Calcium-deficient pool water gets aggressive and will steal calcium from anywhere it can find it. If a source isn't readily available, the water will corrode through all sorts of equipment (like heaters and salt cells) looking for calcium. I always thought corrosion was something to do with chlorine, or that it was just part of managing a pool...but no! It's unbalanced water chemistry.

Add calcium to get the water happily saturated with it, and etching/corrosion problems can be prevented.

How much calcium hardness is ideal?

I personally like my calcium levels between 250-400 parts per million. And no, 400 ppm is not too much. For years I believed calcium hardness was just a minor part of water chemistry. Too much could be a bad thing, and cause scale. Scale is annoying, but guess what? It doesn't damage the pool. Scale is treatable; the opposite problem (corrosion and etching) is not.

I've learned that calcium hardness is the most misunderstood chemistry in the pool business. But the truth is, calcium is a very consistent chemistry in pools; it doesn't fluctuate like pH or alkalinity will. It's a sturdy foundation to balance water around. I learned that from the Orenda LSI app, and what Orenda has been preaching about all year. If you service pools and don't have an LSI app on your phone, you're missing out. It makes water balance so easy. Orenda asked me to talk about this topic because they get a lot of questions about it too. I'm happy to help.

I've heard of people pouring calcium straight into the skimmer...and that's a bad idea. I'm going to explain the easiest and the best way to do this. Beware, when calcium dissolves in water, it gives off a lot of heat. It can burn you.

Add calcium in four easy steps.

You will need:

  • A test kit that measures calcium hardness.
  • A plastic bucket - 5 gallons or about that size.
  • Something to stir with - I use a wooden paint-stirring stick.
  • Calcium chloride - I prefer flakes over prill or granular.
  • A dry measuring cup or bucket - dose properly. Don't cut corners.

Step 1

add calcium, test calcium hardness, add calcium to a swimming poolTest your pool water and your fill water for calcium hardness. Record results. I recommend doing this in the Orenda app, because it lets you email the screenshots of the results with a date and time stamp. I use it to keep track of all my pools and their chemistry. The Orenda app will tell you exactly how much calcium chloride you need. Bring the calcium and the items above to the pool. Measure and pour the right amount of dry calcium into the plastic bucket.

Step 2

add calcium to a pool, dissolve calcium before pouring into poolThen, slowly dip the bucket into the water and let some water into the bucket.  Stir throughout this process and be very careful...this will be very hot. You can burn your hands, and the stick may feel like it could catch fire. Keep the bucket in the water to cool the outside of it. Trust me, it gets hot!

Step 3

add calcium to a swimming pool, UPA, united pool association, Orenda, how to add calciumSlowly add water and stir more and more until the calcium chloride is completely dissolved. You don't want to pour undissolved calcium in the pool, because it can get to the bottom and burn the surface. Let in more water as needed, until eventually the bucket is almost full of water.

Step 4

how to add calcium to a pool, add calcium, UPA, united pool association, Orenda, calcium flake, calcium chlorideSlowly pour the completely dissolved calcium chloride into the pool. I do about half the bucket, then let more pool water into the bucket, and pour again. It helps me regulate the hot temperature of the water, and it also gives me more time to make sure everything is dissolved. Add calcium the right way, and it will go well for you.

What not to do

Don't just throw calcium chloride in your pool. It takes time to dissolve. Putting it in a skimmer or anything else like that is a really bad idea.  Calcium is an alkali earth metal and it's harder to dissolve than some other pool chemicals. If you add calcium my way, you shouldn't have problems. Just remember to be careful because it gets so hot.  Thanks for your time, and thank you to Orenda for letting me share my technique with you.  Good luck out there,



the wrong way to add calcium to a pool, add calcium, calcium prill, swimming pool calcium, undissolved calcium, calcium burns plaster, calcium damage plaster pool What not to do: never throw undissolved calcium in your water! It will sink to the bottom and it gets very hot. It can burn and damage your pool surface. Always pre-dissolve calcium in a bucket before pouring it into your water.


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