Calcium buildup in pool

The causes of calcium buildup in pool interiors are:

  1. High pH in the pool water
  2. The surface has become loose or drummy
  3. Very high calcium hardness
  4. A Calcium nodule has formed inside the surface

Stubborn calcium buildup in pool interiors is often a hard white scale on the pool surface. Calcium is something that many pool owners deal with regularly because it is very hard, stubborn, and difficult to remove. Also, because most pool shops don’t know how to remove it (besides draining the pool) they often suggest acid washing. As a result, most pool shops will recommend draining and acid washing your pool to remove the calcium. While this sometimes works, the calcium usually returns soon after the pool water is refilled. Then, you are right back to where you started! Worst of all, you have now just wasted $1,200 and a lot of water.

The best way to keep calcium away is to properly maintain the pH and alkalinity of the pool water. 

Reduce hardness in pool water

As with every other aspect of water chemistry, calcium hardness also needs to be in balance to protect your pool surface from calcium formation, stains, or corrosion. Unlike pH and chlorine, the calcium level in most pools does not vary greatly over the seasons, so testing every few months is normally enough. Importantly, high or low calcium hardness can cause white staining on pool surfaces, etching, or discolouration. Remember, the trick is to keep the calcium at the right level and to keep the water balanced.  If everyone did this then there would be no calcium buildup in pool surfaces at all.

Calcium hardness reducers

Some inexperienced pool technicians believe that adding a ‘calcium hardness reducer’ will permanently remove calcium buildup in pool surfaces. This is simply not the case because the calcium isn’t actually physically removed from the water with these treatments. What actually happens is that they work by using chemicals to bind up (or capture) the calcium temporarily.  Once the chemical has worn off, then the calcium is simply released and the levels will return to the previous calcium hardness level.

While these treatments do reduce the effects of high calcium in the short term, after 4-6 weeks, the ‘reducer’ chemical is completely neutralized and broken down. A complete waste of time and money. Aside from this, these products will not remove calcium buildup in pool surfaces.

FAQ- Calcium Hardness

What level should my calcium be?

For pebble, quartz, and glass bead pools the suggested calcium hardness level is 200-250ppm.  Suggested levels for fibreglass pools vary depending on the manufacturer but most suggest having it be at least 150ppm.

Does high calcium cause calcium spots ?

As a rule, there is almost no link between calcium levels and calcium buildup in pool interiors.  Calcium stains and spots are usually caused by poor water balance or defective interior application.

Do calcium Hardness reducers work ?

In our experience, calcium hardness reducers appear to reduce calcium levels in the short term.  However, over time the calcium hardness returns to the old levels after the treatment has burned out.

does calcium effect water quality ?

Calcium-rich water is called ‘hard’ water.  This is because the calcium content is very high.  Low calcium water is called ‘soft’ water which feels much nicer to swim in. Best to keep the calcium within the right range.

How do I increase calcium hardness?

Calcium hardness is increased by adding calcium chlorite from the pool shop.  It is very cheap to buy and easy to add.  Your pool shop will help you know how much you need based on a water test.

How do I reduce calcium hardness ?

To reduce calcium hardness permanently is best to partially drain the pool water and refill it.  This process removes high-calcium water and replaces it with low calcium tap water.

Calcium Nodules

Calcium nodules in a swimming pool are a common issue that can occur on many types of pool surfaces. These are typically caused by an excess of calcium in the pool water, which can accumulate and form hard deposits on various surfaces. They can also form from voids in the pool pebbles that allow water and calcium to form behind the pebbles.  Over time, the calcium in these voids will continue to grow and push through the pebble.  The picture below shows what this looks like up close.

Preventing calcium nodules is generally easier than removing them once they’ve formed. Regular maintenance and proper water chemistry are key to keeping your pool surfaces free of these deposits. Additionally, if you’re unsure about how to address calcium nodules or are dealing with a severe case, some companies have products that can soften and dissolve nodules without draining the pool.

The best way to prevent these nodules is to keep the pH of the water balanced (7.4) and the calcium hardness at the right level.  Calcium hardness that is very low or very high can cause nodules to form faster than normal.  For most cement-based interiors, calcium hardness should be around 200-300ppm.  Gently rubbing the nodules with a pumice stain will also help remove them.  

Calcium Nodule

Causes of Calcium Nodules

Delamination is one of the primary causes of calcium nodules is the delamination of the pebble finish. When the pebble finish plaster separates from the concrete pool shell substrate, small pockets form. Water can infiltrate these pockets and leach calcium hydroxide from the cementitious material. As this water reaches the surface of the pool, the calcium hydroxide reacts with carbon dioxide in the air to form calcium carbonate, which presents as calcium nodules.

Improper Chemical Balance  An imbalanced pool chemistry, especially consistently high pH and calcium hardness, can contribute to calcium nodule formation.

Spot Etching caused by aggressive water can remove the smooth finish of the pool interior and create small pockets where calcium can deposit and form nodules.

"If you are not physically removing the calcium from the pool water then your calcium reducing treatment will only be temporary"
Aussie pools logo
Wade Bosse
Founder - Aussie Pools
Calcium on quartz pool

Calcium in pool water won’t cause calcium spots

Many parts of the country have different calcium levels in their tap water. For this reason, many pools can have varying calcium levels in their pool from the beginning. Generally, high calcium levels will not affect your pool surface in the short term, if the water is balanced. This is because balanced water helps to keep calcium suspended in the water. In this condition, it will not plate out, or precipitate onto the surface.

 If your calcium hardness level is high then bringing it back to the right range will definitely help in the long term.  Calcium hardness (and mineral hardness) is usually an ongoing issue if bore water is being used in your pool. We have more detailed information about calcium on this page.

Final thoughts…

Just like most things, calcium hardness is about balance.  Very low calcium will literally destroy your pool finish.  High calcium hardness will cover the pool surface in cas=lcium over time.  The trick is to keep it within the right range.  Doing this will make the water feel nice to swim in and keep your surface smooth for a very long time.