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How To Lower Calcium Hardness in Your Pool: 6 Effective Tips

Calcium hardness prevents the plaster from corroding, but too much calcium causes buildup and stains. It’s important to keep your pool’s calcium levels around 320ppm. Failure to regulate the calcium can wreak havoc on your pool’s heater, salt system, and pump. Fortunately, it’s quite easy to reduce it.

To lower calcium hardness in your pool, follow these steps:

  • Test the calcium hardness
  • Brush the pool
  • Add descaling chemicals
  • Drain and refill the water
  • Dilute the pool with evaporation
  • Clean the salt cell

In this post, I’ll explain how you can test and adjust your pool’s calcium hardness levels. I’ll also dive into the importance of maintaining optimal calcium levels to prevent stains, buildup, and more.

Test Your Pool’s Calcium Levels

Always test your pool’s calcium before adding calcium hardness or draining the pool. Most pools have a little bit of calcium from chlorine, plaster, and other additives. Saltwater pools are prone to calcium buildup, so they need to be tested more often.

Here are your three testing options:

  1. Use test strips. Test strips are the most affordable option. You’ll receive enough to test the water for one to two swimming seasons. The only downside is that they expire quicker than any other testing method.
  2. Try test drops. These reagents only require about five drops per use. You can use them to test the calcium, chlorine, pH, and many other pool chemicals. Many people rely on test drops for their accuracy, though they’re a bit pricier than the strips.
  3. Consider digital test meters. While these meters don’t test everything, they often cover the calcium hardness. Some meters are permanent installations, while others are used with test strips for accurate readings.

The Varify Premium Water Hardness Test Strips are extremely accurate and easy to use. Dip one strip into your pool or spa for nearly instant results. Each bottle includes a color range that tells you whether the water is too hard, too soft, or perfect.

Varify Premium Water Hardness Test Strips

Brush Your Swimming Pool

I suggest brushing your pool one to two times weekly. Regular brushing reduces calcium buildup and algae blooms. Those with vinyl and fiberglass liners should opt for a soft bristle brush, while people with plaster pools can use a stiff brush or a wire brush. Using the right brush can remove calcium deposits from the tiles, walls, and bottom of your pool.

Brushing the pool doesn’t remove calcium hardness from the water, but it prevents the deposits from leaching more calcium into the pool. It’s crucial to scrub the walls and tiles until there’s no more calcium left. You can also use pumice stones, or an abrasive sponge dipped in muriatic acid. If you choose the last option, always wear protective gloves and goggles.

The Pool Blok is a dense pumice stone brick. You can use it to remove calcium, lime, and other stains. There’s no need to replace the brick too often since it’s dense enough to scrub the whole tile line. You can also connect it to extended pumice block holders.

Pool Blok

Add a Descaling Chemical

Descaling chemicals are great because they remove lime, calcium, and other buildups without using brushes or pumice stones. You can brush the descaler after it settles, but they work best with proper pump circulation. Keep in mind that not all pools have calcium hardness issues. Calcium buildup is one of the main differences between vinyl liners and gunite pools.

EasyCare Scaletec is a top-shelf solution that gently removes lime, scale, calcium, etc. A one-gallon bottle will clear your pool’s calcium buildup in less than four weeks. You can also use this descaling solution to remove the buildup in your salt system. It’s the perfect all-around treatment without requiring muriatic acid washes.

EasyCare Scaletec

Keep these things in mind when using descaling chemicals:

  • Never use more than the manufacturer recommended. Excessive amounts of descaling chemicals can stain the walls and cloud the water.
  • Run the pump several hours each day for at least one month. Descaling chemicals need to circulate throughout the day for the best results.
  • Always keep the water above the highest calcium stains. These treatments only work if the calcium stains are underwater.

Much like brushes, pumice stones, and acid washes, descaling solutions only remove the calcium buildup. They can’t reduce the water’s calcium hardness, but they can prevent it from increasing.

Partially Drain and Refill the Pool

The only surefire way to reduce the pool’s calcium hardness is to drain and dilute the water. Diluting the water will drastically lower the calcium, but it’ll also affect every other chemical in the swimming pool. I always provide the following four suggestions to pool owners who have high calcium hardness:

  1. Never drain more than ⅓ of the pool. Draining your pool too much can cause caving, cracks, dryness, and other unwanted side effects. Instead, drain a couple of feet, refill the pool, test the calcium, and repeat if necessary.
  2. Test the chemicals after refilling the water. Everything will change when you dilute the water. Draining the pool is one of the only two ways to lower cyanuric acid. It’ll also lower the chlorine and potentially increase the pH.
  3. Calculate how much calcium hardness needs to be removed. Find the average depth of your pool, then determine what percentage needs to be drained. For example, if your pool’s calcium level is 25% above 320ppm, you could drain ¼ of your pool.
  4. Turn off the pool pump until the water is above the skimmer basket. Running the pool pump when the water is below the highest inlet will cause cavitation and invite air into the plumbing. Both of these issues will ruin the pool pump, heater, filter, etc.

Dilute the Water With Evaporation

Evaporation is a slower method than the previous example. Draining and refilling the pool can be done within a day. However, most pools evaporate at a reliable rate. If your pool loses about 2 to 4 inches of water weekly, you can refill it with hose water. This lengthy process takes a month or so to reduce the calcium hardness.

Keep in mind that some water sources have calcium. I recommend testing the hose water for calcium before adding it to the pool. The last thing you want is to increase the calcium hardness if it’s already too high. Instead, you can use rainwater or well water. Another option is to distill the water, cool it, and pour it into the swimming pool.

If you want to dilute your pool’s calcium hardness, remove all solar covers and solar rings. They drastically reduce evaporation. I also suggest running your pool’s heater, even if it’s warm outside. The increased water temperature evaporates tons of water, letting you dilute the pool much quicker.

Clean Your Pool’s Salt Cell

If you have a salt system, the cell needs to be cleaned about three times per year. Cleaning the salt cell will reduce the calcium buildup. An excessive amount of salt and calcium will raise the pool’s pH, calcium hardness, and alkalinity. Rinse the salt cell in a mixture of 1 part of muriatic acid to 4 parts of water.

Those without salt systems should monitor the pool’s salinity. Too much salinity will increase the pH, alkalinity, and calcium (much like salt cells). Almost all pools have trace amounts of salt due to various chemicals in the water. For example, liquid chlorine is sodium-based. Using too much liquid chlorine without removing the pool cover will drastically increase the pool’s salinity.

Calcium needs to be perfectly balanced to maintain a healthy, clear pool. Too much or too little calcium hardness need to be adjusted accordingly.


  • Jonah Ryan

    Jonah has worked for several years in the swimming pool industry installing and repairing equipment, treating pools with chemicals, and fixing damaged liners. He also has plumbing and electrical experience with air conditioning, ceiling fans, boilers, and more. When he's not writing for Temperature Master, he's usually writing for his own websites, and

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