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Calcium Hardness In Swimming Pools

Calcium Hardness In Swimming Pools

It is the goal of this article to help you understand calcium hardness as it relates to your pool or hot tub with very little chemistry. Understanding calcium hardness will help you increase the lifetime of your pool and hot tub. This includes the actual pool and hot tub and all of the accessories, plumbing, pumps, heaters, lighting, and just about everything else the water touches.
Calcium hardness is a part of "total hardness". We'll stick with just calcium hardness in this post because it is the most important part of total hardness for pool and spa owners. A healthy calcium hardness test value is 300 ppm  for swimming pools and 200 ppm for hot tubs. 

Corrosion vs Scaling


Over time you will notice the affect of unbalanced calcium hardness on your pool or hot tub. There is a formula called the saturation index formula, SI for short. This formula takes into consideration pH, alkalinity, calcium hardness, dissolved solids, and water temperature.  When the SI value is zero the water is balanced. If this value dips slightly into the negative (say around -0.3ish), the the water can become corrosive. Corrosive water chemistry will degrade your concrete, grout, plaster, and even the metal in your pump and plumbing. You have probably seen this damage around old swimming pools. Sometimes the damage is so bad you can feel the concrete crumbling under your feet.
Although it does take time for serious conditions to surface, corrective repairs for this kind of damage can be costly. It could mean resurfacing or re-tiling your pool or replacing your pump or heater. 


pool scale on tileOn the other hand, if your SI pushes slightly above zero (say around 0.5ish) then the water chemistry is favorable for scaling. Simply put, the calcium comes out of the water solution and attaches to tile, concrete, plumbing, and metal.
Again, it is likely that you have seen examples of scaling around older concrete and tile pools and hot tubs. The scale is typically white to off white in color. It often forms along the waterline. Besides being a little unsightly, the scale is difficult to remove from tile and concrete. Scale in plumbing could require complete replacement. 

Preventing Scaling In Pools and Hot Tubs

Raise Hardness in a hot tub or pool

If you find that you have lower than balanced calcium levels in your pool, you can add a calcium hardness product. These products are formulated with calcium chloride. Sometimes called calcium increasers, these products are granular and are spread across the water's surface. A calcium increaser will increase your pool or hot tub's calcium levels. 

Lower Hardness in a Hot tub or Pool

Lowering calcium levels is a little more difficult. To lower levels, you have to actually remove calcium from the water. Here's a tip, it's almost always easier to add something to water than to remove something from water. However, you can add a calcium sequestering agent to the water. These products are formulated to bind with calcium, locking it up to prevent it precipitating out of the water and attaching to surfaces. 

Occasionally adding clarifier to your pool can also help prevent scaling. Clarifiers will cause calcium to clump together. These clumps can be large enough to be removed by your filtration system. 

The Recap About Calcium Hardness

calcium scale in pvc pipes

Calcium hardness balance is an important part of water balance. When calcium levels are to low your water will attempt to draw calcium out of your concrete, grout, and tile. This process can cause damage that can be very expensive to repair. Low calcium levels can also corrode your plumbing and equipment. 

When calcium levels are too high, calcium deposits called scale can attach to your tile, concrete, plumbing, and metal filter and pump parts. Many consider scale to be an eyesore and it's really hard to remove. If your plumbing and equipment have excessive scaling they may need to be replaced. 

The best way to control your pool or hot tub's hardness is regular testing. This way you identify water balance issues before they cause any damage.  

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Balancing Your Swimming Pool Water


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