What is Calcium Hardness?

What is “calcium hardness” and “total hardness” and what’s the difference between them?

Calcium hardness is the measurement of dissolved calcium in hot tub or pool water. Total hardness, which is measured by different test kits, measures both the calcium and magnesium present in water. Calcium hardness can be measured on its own by drop test kits or handheld photometers like the Lamotte Color Q Test Kit.

What is the Saturation Index?

The SI formula considers relationships between four chemicals in your pool and spa water and two physical attributes—calcium hardness, alkalinity, total dissolved solids, cyanuric acid alongside pH and water temperature. When the SI value is zero, the water is properly balanced. If it falls on either side of that number, the water is becoming unbalanced and becomes either corrosive (negative) or will scale your surfaces (positive).

What should be my water’s calcium hardness range be?

The recommended range in a hot tub or pool is between 200 and 400 parts per million. That number may vary depending on the hot tub finish and chemicals using to treat the spa.

If your spa is acrylic and you use bromine to treat the water, the recommended level of total hardness should be between 175-225 ppm. For those using the digital test kits, that level will fall somewhere between 100-300 ppm.

Another factor that determines appropriate hardness levels is water temperature. The colder the water, the more calcium is needed to maintain levels.

What problems can occur if hardness is too low?

Water that has low hardness levels becomes corrosive, etching plaster, attacking concrete, metal and all other surfaces it touches. It can cause pitting and surface stains and may color water caused by metal pulled out of piping, fittings, and other pieces of equipment. Not a good look.

What problems can occur if hardness is too high?

The excess amount of minerals gets to the point where the water can’t “hold” all of it and has to deposit it elsewhere. High calcium hardness means that your water will turn cloudy unless the alkalinity and/or pH are low enough to compensate for it. Excess calcium carbonate also causes a myriad of other unsightly problems, including creating a crusty, grayish white scale buildup on surfaces, piping, and other equipment.

Its roughness can also cause abrasions on the skin of hot tub dwellers and snag on swimming suits. Another problem is it becomes a good breeding ground for microorganisms—yikes.

Calcium carbonate can be significant enough to clog filters, reduce circulation and increase pressure when it builds up in piping, and makes a hot tub’s heating unit less and less efficient.

How often should I be testing the hardness levels of my water?

You should be assessing the hardness levels in your water once a month, more if you have clouding or scaling in your water.

How to I test my Total Hardness levels?

There are a few test strips and kits that will test for total hardness. These are AquaChek Bromine Test Strips, AquaChek Select Test Strips, AquaChek Pro Total Hardness Test Strips, Taylor K-2005, Taylor K-2006, Lamotte ColorQ 2056 and 2057. Testing for hardness levels using these products is a snap and will protect your hot tub and prevent unnecessary expenses for repairs of your hot tub.

How to I fix my levels if they’re too high or too low?

If your hardness is too low, you can add Spa Pure Hardness Increaser or ProTeam Calcium Up.

If your hardness is too high, you'll probably have to entirely drain or partially drain the vessel and replace it with softer water. Part of the problem may be that your fill water has high calcium and you may need to use a pre-filter to help remove these minerals when refilling either your pool or hot tub. Try testing your fill water before adding it to see if this is necessary.

You can also try to balance the chemistry out by lowering the pH and alkalinity. That can be a bit tricky, though.

How do I test my calcium hardness levels?

Since test strips can only measure total hardness, a drop test will allow you to approach the true concentration of calcium hardness in 10-ppm increments. To do a drop test, fill a test cell with sample water, add buffer and indicator reagents, and gently swirl to mix them. The water will turn red if calcium hardness is present.

Next, add the calcium hardness reagent, swirling and counting each drop until the color changes from red to blue. Multiply the number of drops it took by the equivalence factor in the test instructions to determine the calcium hardness level. The reading is expressed as parts per million of calcium carbonate.

If you want to take out the guesswork, consider investing in photometer that does the analysis for you.

How can I prevent additional scale buildup?

If you’re looking to lower calcium hardness levels (or that doesn’t seem to help on the surface of your hot tub or pool), there are a few such products you can use that will help to prevent scale buildup: Spa Pure Stain and Scale Preventer, ProTeam Metal Magic. Add a small dose each weak to protect your spa from calcium buildup that can damage your jets, heaters, and other equipment components.