Pool Calcium Hardness

Understand Calcium Hardness & Pool Water Maintenance. Learn Swimming Pool Water Chemistry & Hard Water Solutions.

The ideal range for perfect swimming pool chemical maintenance is 150 ppm-250 ppm, not 300 - 350 ppm or higher. This is especially true for saltwater pools and salt water pool system. If you add any more calcium hardness increaser your salt cells might calcify and burn up, shortening its life. You also run the risk of having hard water scale at the water line.

Water is hungry for calcium and will try to feed its appetite any way it can. Many times it will draw it from the plaster, which causes unsightly pitting, or from your filtration system, which will cause hard water deposits.

Maintaining your pool's calcium hardness level between 150 ppm - 250 ppm will prevent this from happening. Some areas of the country may have very soft water or very hard water.

You don't need take your tap water anywhere and have expensive tests performed. Simply call your local water company and ask them the calcium hardness of the water or use a good pool water test kit. 

Central Oregon has very very soft water, about 1 ppm - 2 ppm. Places like Arizona, Nevada, Florida, and Southern California might have water hardness that can reach 200 ppm-300 ppm or even higher.

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If you have a Hot Tub, spa, or heated pool, maintaining the proper calcium hardness in your water becomes even more critical.

Most swimming pool problems result from bad pool chemistry advice given at the wrong time.

Problems With Low Calcium Hardness

  • Pitting and etching of the plaster
  • Dissolved grout in your pool
  • Staining of the pool surface
  • Possible heater failure
  • Corrosive and scaling water
  • Supersaturation
  • Swimming pool stains

Problems With High Calcium Hardness

  • Skin and eye irritation
  • Cloudy swimming pool water
  • Clogged pool filters
  • Poor filtration
  • Calcium build-up and corrosion on heaters
  • Scaling of the pool water

This is according to the Langelier Index that has been used for above ground pool maintenance, inground pool maintenance, and salt water pool maintenance for decades. Keep in mind, proper balance of your swimming pool chlorine, pool pH, pool alkalinity, and hardness is of the utmost importance in having a safe and clear pool water. It will decrease your chlorine demand, muriatic acid use, pool stabilizer, and alkalinity increaser. 

One easy way to slow the progress of calcium rings at the water line is to keep the pH a bit more acidic, about 7.2 - 7.4.

Tap Water Calcium Hardness

calcium hardness,langelier index,hard and soft water,swimming pool stains,pool water chemistry

When you have softer water, you may need to add Calcium Chloride to correct the hardness level. DO NOT make slurry or mix the calcium chloride in a bucket with water. It may “steam” up and cause severe burns. Have a designated chemical bucket pool pole to stir up other chemicals. 

Also, when you add the calcium, you might have cloudy pool water. This is normal and should clear up with a few hours of filtration. If you have a salt water swimming pool with an in-line chlorine generator, be extra sure your calcium is at the correct level or else you may end up ruining your salt cells. The calcium will crust on the fins and before you know it, you're shelling out another $1000 for a new salt chlorine cell.

Broadcast it directly into the pool, starting in the deep end and working around the perimeter of the pool. Apply the calcium as you would use a salt shaker. Refer to the chemistry help chart to see the amount calcium chloride your pool needs for your pool water care.

Any store that sells swimming pool equipment supplies or discount pool chemicals can help with your calcium needs. 

Hard Water And High Calcium Fill Water

Having high calcium hardness (above 250-300 ppm) in your tap water is very difficult to keep down. Reducing calcium hardness is difficult. You may either replace some or all of your pool water or have pool water trucked in.  

When filling your pool with fresh water, be sure to test the tap water for its hardness. This will give you a good starting point to see if you need to add calcium chloride or not. Unfortunately there is no quick and easy answer on lowering your swimming pool water hard water.

Chart - Raising Hardness With Calcium Chloride



(ppm) 1,000 5,000 10,000 15,000 20,000 25,000 50,000
10 2 oz. 10 oz. 1 1/4 lbs. 1 3/4 lbs. 2 1/2 lbs. 3 1/4 lbs. 6 1/4 lbs.
20 4 oz. 1 1/4 lbs. 2 1/2 lbs. 3 3/4 lbs. 5 lbs. 6 1/4 lbs. 12 1/2 lbs.
30 6 oz. 1 3/4 lbs. 3 3/4 lbs. 5 1/2 lbs. 7 1/2 lbs. 9 1/2 lbs. 18 3/4 lbs.
40 8 oz. 2 1/2 lbs. 5 lbs. 7 1/2 lbs. 10 lbs. 12 1/2 lbs. 25 lbs.
50 10 oz. 3 lbs. 6 1/4 lbs. 9 1/2 lbs. 12 1/2 lbs. 15 3/4 lbs. 31 1/4 lbs.
60 12 oz. 3 1/4 lbs. 7 1/2 lbs. 11 1/4 lbs. 15 lbs. 18 3/4 lbs. 37 1/2 lbs.
70 14 oz. 4 1/4 lbs. 8 3/4 lbs. 13 lbs. 18 3/4 lbs. 22 lbs. 43 3/4 lbs.
80 1 lb. 5 lbs. 10 lbs. 15 lbs. 20 lbs. 25 lbs. 50 lbs.
90 1 lb. 5 1/2 lbs. 11 1/4 lbs. 17 lbs. 22 1/2 lbs. 28 lbs. 56 1/4 lbs.
100 1 1/4 lbs. 6 1/4 lbs. 12 1/2 lbs. 18 3/4 lbs. 25 lbs. 31 1/4 lbs. 62 1/2 lbs.

Pool Water Testing For Hard Water

What is pool water hardness?

Water hardness is the makeup of the minerals (calcium, magnesium, iron, etc...) that are naturally found in tap and pool water.

When do I test for water hardness?

The best time to take any tests is in the late afternoon or early evening. Maintain your pool’s hardness level between 150 ppm-250 ppm, not 350 ppm or above if you can.

Where do I test the water hardness?

The best place is either in the deep end of the pool or the furthest place from the filtration. Be sure to test you tap water as well so you’ll have the proper starting point with a freshly filled pool.

Why should I test for hardness?

Water hardness is one of the elements that make up the test routine. Included in this are chlorine, combined chlorine, CYA/pool stabilizer, pH, and alkalinity. Water is hungry for calcium and will take it from any source it can get. By keeping your water’s appetite for calcium fed and at the proper levels (if your fill water has low calcium hardness) you will minimize corrosive and scaling water, pitting of the plaster, clogged heaters and filters, and eye and skin irritation.

These pool tips will save you time, money, and maybe even a few migraine headaches.

Go swim and have fun with your family and friends.

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