Calcium Hardness in Swimming Pools

by Pool Builders on 12-26-2009 in Articles

Calcium hardness or CH for short, is the measure of the amount of dissolved calcium content present in your pool water. Calcium as we know it is a mineral that is naturally present in water and it is usually found in high concentrated levels. Whenever your pool or spa has high concentrations of calcium present, you have what is called hard water. On the other hand when the calcium level is low, you will have what we call soft water. to properly manage your pool water chemistry, you must remember that total hardness and calcium hardness in a spa or pool are different; although, they are related entities.

Total hardness is the sum of calcium, magnesium, iron, manganese, and other elements found in your water facility. It is usually expressed in grains of hardness (i.e. 1 grain = 17.1 ppm).The calcium hardness in swimming pools and spa water systems is ordinarily measured as calcium carbonate. However it is not in solution, calcium carbonate is exhibited in your pool and spa as scale. This is a white scale formation that is also a type of natural salt. This scale like salt can be found in nature in the form of one of the following

  • Chalk.
  • Calcite (check spelling).
  • Aragonite.
  • Limestone.
Calcium carbonate is not very soluble in water and unless your pool water chemistry is properly maintained, it can drop out of solution very easily. Another concerned behavior that pool owners and operators have with calcium, is that unlike most other pool chemicals, it becomes less soluble as the temperature goes up. Because of this basic understanding, proper management of hot water systems become more perplexed.

In order for you to maintain proper water chemistry in your swimming pools, your calcium hardness level should always be in the range of 200 to 400 ppm. If the level of the hardness in your calcium content rises above 400 ppm, you must take extreme measures to maintain your total alkalinity and pH at lower levels. This is a precaution that will help you avoid any scale formation in your pool and spa. This is an absolute must if the water in your aquatic facility is heated. You will be faced with an impossible task of maintaining your pool or spa water balance, if your Calcium level reaches 1000 ppm.

When your calcium hardness is too low!

Whenever the CH level in your swimming pool or spa is too low, the water in your facility will become very aggressive or very corrosive. Low levels of calcium is also a major contributor to foaming in spas or hot tubs. This is a pool water problem that is not good for the plaster or concrete surfaces in your pool or spa. The truth of the matter is that you should test the calcium content in your water regularly and if it is too low, take the necessary steps to correct it at once. Failure to take action, will result in your water having the capacity to leech or dissolve calcium carbonate from your pool and spa surfaces.

Pool and spa water that is corrosive, will lead to some very costly damages to their surfaces. Some of the problems that can occur are as follows:

  • Etching or pitting of your pool and spa surfaces. This water problem can occur in a very short time period if you fail to monitor your pool water chemistry.
  • Staining of your pool or spa surface walls.
  • Failure of your pool or spa heating system.
Raising your CH levels

It is reported that low levels of CH or soft water is a major contributor to a lot of surface damage to pools and spas around the country. So once you have done a calcium hardness test and determined that you have to take immediate steps to raise it, the required pool chemicals must be added. The recommended pool chemical of choice for this task is calcium chloride. This pool chemical comes in two different forms which are sold at different strength as well.

  • Hydrated Chloride is the first of the two that we will mentioned. This pool chemical can be purchase at 77% strength.
  • The next one is the anhydrous calcium chloride. This is one of the two pool chemicals that you can get at full strength if you so desire. It is sold at 100% full strength.
It does not matter which of these two pool chemicals you choose, just remember to read the manufacturer warning and instructional labels. This is for your safety because both of these calcium chlorides can generate a significant amount of heat when they are added to water. For this reason a good practice to get into is, to dissolve either one of these pool chemicals in a bucket of water and thoroughly mix them prior to slowly adding them to your pool and spa.

Now depending on which one of these two calcium chlorides you decide to use, the rate at which you will added it to your pool/spa, will be determine by the their strength. For instance, if you use the 77% strength hydrated calcium chloride, your rate of addition will be at 1.25lbs for every 10,000 gallons of water. A calculation for this dosage will help you achieve a 10 ppm increase in your CH level.

On the other hand, if you decide to use the 100% strength anhydrous calcium chloride your rate of addition will be a little different. For this chloride your dosage will be 1.0lbs for every 10,000 gallons of water. Again the calculation for this dosage will give you a 10 ppm increase in your calcium content level.

When your calcium hardness is too high

High levels of calcium in a swimming pool or spa can be just as problematic as low levels. Truth be told, balancing your pool or spa water is not an easy task but nevertheless this is vitally important. Not only for your pool but also for the many swimmers that will be using your water facilities. We have found that it is much easier to lower the pH or total alkalinity in your pool than it is to lower your calcium content.

Lowering your pool/spa calcium content can be very difficult. Why? Because it usually involves you partially draining and replacing your existing pool water. To help maintain a low level of calcium after partial drainage, you have to use a source or make-up water that has a low level of hardness. However if you conduct a calcium test to determine the hardness of your make-up water and found that it is too high, you can allow the water to pass through a water softener prior to entering your pool/spa. Once the water passes through the water softener, it will reduce the level of hardness found in the water before it enters into your pool or spa.

Problems caused by high calcium content

High levels of calcium will result in scaling water. Other problems include the following:

  • Your pool or spa surfaces will become very rough. This condition can harbor bacteria or scratch the skin of your bathers.
  • Your pool or spa filters can become clogged very quickly; thus, reducing your filtration capabilities and increasing your backwashing (filter cleaning ) frequency.
  • Your pool water will become or look very cloudy. This is the same condition that is experienced when your alkalinity is too high.
  • Your pool spa heater element can become clogged as well. This problem can eventually cause you to replace your pool heater system.
  • You will experience a reduction in your pool or spa water circulation. This will lower or reduce your pool or spa turnover rate considerably.Your swimmers will complain about eye and skin irritations.
When it comes to balancing the water of a swimming pool/spa, the pH is will be the most influential variable in the CSI; however, the calcium content is the most important. This means that a significant amount of calcium present in your pool water is an absolute necessity. Therefore you have to maintain a well balance saturation index at all cost.

If the case of hardness of calcium levels that are too high, you can lower your pH range and your total alkalinity levels to compensate for it. Also, to prevent any type of scale formation or keep your calcium content in solution, you can use some sort of sequestering agent. This chemical will help by interfering with the development of calcium carbonate crystal (scale) formation. Again, please remember to read and follow all the directions found on the labels of all pool chemicals.

That way you will learn the potential dangers of the chemical you are about to use and the necessary safety procedures to avoid any miss use of it. And remember that you should never add water to pool chemicals. Instead add pool chemicals to water, especially when dealing with pool chemicals like calcium chloride.

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