Calcium Hardness: What You Need to Know


by Rick Patterson

Depending on where you live, you may have heard about ‘hard’ and ‘soft’ water and how they affect your family and home. Maybe you’ve already had to take steps to adjust the quality of your tap water using salt softeners or filtration. If you haven’t heard those terms before… no, we’re not talking about ice or fluffy water. It’s all about the minerals hiding inside.

Did you know that having hard or soft water can negatively affect your pool too? As with all things, the calcium hardness levels in your pool need to be checked, rechecked, and properly balanced to protect your pool equipment, plumbing, and the pool itself. 

What Is Calcium Hardness? 

The term ‘calcium hardness’ refers to the measurement of how soft or hard your pool water is, as well as how much dissolved calcium is floating around in there. Professional pool services use the LSI (Langelier Saturation Index) or pool water saturation index to measure how saturated your pool water is with calcium, magnesium, and other metals.

If you have high calcium hardness levels in your pool, there’s a good chance you live in an area with hard water. Hard water is groundwater that has come into contact with an abundance of calcium and magnesium, causing a highly-mineralized solution to form from the dissolved solids.

On the other end of the spectrum, we have soft water which is demineralized water that contains low levels of minerals. Having water on either extreme can wreak havoc with the pH of your pool water, destabilizing your carefully balanced pool. 

The good news is that neither of these types of water is the end of the world when it comes to pool care. With frequent testing, proper maintenance, and a few pool care tricks, you can keep your levels in-check year-round with minimal effort.

What’s a Good Range? 

I’m so glad you asked. Keeping your calcium hardness levels between 200 and 400 ppm (parts per million) is a good rule, but 300 ppm is the sweet spot. Remember, if your levels go a bit too far in either direction, it can mean serious problems for your pool down the road.

How Calcium Hardness Affects Your Pool

The quality of your pool water is directly related to the calcium hardness levels. Too low and your pool equipment and concrete will quickly corrode, costing you a lot of money in repairs and replacements. 

If the calcium hardness levels are too high, you might jump in for a swim, only to discover gross scaly buildup floating around with you. Not only that, but calcium deposits can build up in your pipes, clogging up plumbing and rendering your equipment useless.

If the calcium hardness levels in your pool are too high or low for extended periods of time, it can actually reduce the effectiveness of the sanitizer and other chemicals you add to the pool water. Maintaining proper calcium hardness levels, just as you do with your pH and sanitizer levels, is a great way to keep your pool looking and feeling its best.

How Frequently Should You Test?

As a responsible pool owner, you probably know that testing your pool chemistry 2-3 times per week is one of the best ways to keep your pool clean, safe, and balanced. The good news is that calcium hardness tests don’t need to be conducted quite so often.

You may already be using test strips to check your pool’s chemistry but unfortunately, these don’t test for calcium hardness. To check the degree of dissolved calcium in your pool, you’ll need to get a liquid test kit or complete test kit to measure accurately.

In some instances, you’ll have some visual cues as to whether your calcium hardness is too high or low but sometimes it won’t be obvious to the naked eye, which is why periodic testing is so important.

What If Your Water Is Too Hard?

If your water is too hard, you’ll notice that your once-crystal-clear pool is now cloudy with minerals. The sides of the pool might have a new layer of scaly build-up and who knows if that junk has already made it to the pipes? 

What If Your Water Is Too Soft?

Uh oh. You’ve tested your water only to discover that your calcium hardness levels are below 200 ppm. You won’t be able to see any noticeable changes in your pool if your water is too soft but it can cause unseen and damaging corrosion to your pipes and concrete.

In either of these situations, your pool is actually trying to balance itself out. With too little calcium, it may try to find it by eating into the plaster of your pool walls. With too much, it tries to shed it in the form of the scaly deposits in your water and pipes. It wants to be balanced and is effecting chemical reactions to get back where it needs to be.

Find Your Balance: Managing Calcium Hardness

Don’t worry, we’re not doing yoga today. 

No matter which situation you’ve found yourself in after testing your pool water, the best way to fix the problem is with proper balance. Balancing your pool water starts with the classic steps of pool maintenance. 

  1. Clean: Start by thoroughly cleaning your pool. This means turning on the filter and vacuum, emptying the skimmer basket, and grabbing your skimmer net and pole to pick up anything floating on top. A good deep-clean is a great way to get your pool back into balance.
  2. Test: Next, do a routine pool water test to check your chemistry. Be sure to pay close attention to the pH and total alkalinity. If these are out-of-whack, there’s no chance of fixing any calcium hardness issues you may have. 
  3. Balance: Lastly, balance your pool water with the information you got from the test. If your levels were in-range, perfect! You’re good to move on to adjusting the calcium hardness levels.

How To Increase Calcium Hardness in Your Pool

Let’s start with the easy one. Increasing the calcium hardness is a one-step operation. To get your levels back to where they need to be, simply get a container of calcium hardness increaser to add to your pool.

This handy product, which is usually a solution of calcium chloride, will do all the work for you. Just make sure to follow the manufacturer’s instructions for best results.

3 Ways to Decrease Calcium Hardness in Your Pool

Okay, this one is a bit trickier but still very achievable. If you live in a place with terminally hard water or your chemistry just went wonky, you have three options for how to solve the problem.

1. Drain Some Water

Draining water from your pool and refilling it with fresh water is a good way to decrease the calcium concentration in your pool. This one only works if you live somewhere that doesn’t have hard water to begin with. If your tap water at home is on the softer side, however, this will work wonders to lower the total calcium hardness in the pool.

2. Make Friends With Flocculant

For pool owners with hard water, flocculant could be your best friend. Adding this powerful stuff to your pool actually clusters all of the excess calcium in your pool into concentrated blobs. Now you can easily vacuum and skim it out, cleaning your walls and backwashing your filter to complete the task. 

3. Throw Acid On It

Okay, that came out wrong, but acid may actually be the solution here. You may have some muriatic or dry acid (sodium bisulfate) lying around with your pool supplies but if not, they are relatively inexpensive and easy to find. 

This combination may help to balance your water according to the LSI or pool saturation index we mentioned earlier. This should be your last option because muriatic acid doesn’t actually decrease the dissolved calcium levels in your pool water and may make your pool water overly acidic and corrosive.

It’s a good idea to chat with a pool care expert before attempting this option as it has the potential to throw your pH and general pool chemistry all out-of-whack. If this is your last resort to decrease your calcium hardness levels, make sure to pay close attention to the manufacturer’s instructions for adding the acid, based on the capacity and type of pool you have. 

Achieving Balance

Keeping the water in your pool balanced properly all-year-round can be a delicate dance to master. The first step, however, is discovering what type of water you’re dealing with and making the necessary adjustments from there.

Whether your home has hard water, soft water, or something in between, knowing is half the battle. With consistent testing, some helpful water supplements, and vigilance, you can relax knowing that your equipment is safe from corrosion and that gross, scaly build-up is a thing of the past.

Categories: Pool Care, Pool Chemistry