How you remove calcium scale from a pool depends on the extent of the scale, where it’s located in the pool and the type of pool surface. This is one problem you need to be aware of and have under control because scale can damage the pool equipment.
Calcium carbonate scale is a hard crystalline substance that bonds to your pool surfaces and equipment like concrete. Many people don’t notice the scale in their pool as the deposits are off-white or clear and not easily seen on plaster and aggregate surfaces. Small deposits of scale can be cleaned away by brushing or sanding the pool surface. Larger deposits require emptying the pool and acid washing the surface.
The accumulation of scale is more serious in your pool filtration system, heater and chlorinator cell as it will damage the equipment. The equipment requires regular inspection and periodic acid cleaning to remove these crystalline calcium deposits.
Table of Contents
What is Calcium Scale in a Swimming Pool?
Swimming pool water can become saturated with calcium compounds that come out of solution and crystalize on pool surfaces and equipment. This process commonly produces a clear or white-looking lime scale build-up around the waterline but scale will also crystalize on the walls and steps.
Scale deposits can also form inside your pool plumbing, filter tank, water heater and chlorinator unit. When this happens clean these components otherwise they will operate with a reduced capacity or fail completely.
Calcium carbonate or calcium silicate crystals can form rapidly even when the pool chemistry is balanced and the water is clean and clear. Usually the crystalline deposits are caused by hard water from your local water supply, a higher than normal pH and high total alkalinity.
What Causes Calcium Scale to form in a Pool?
High calcium hardness, high pH and high total alkalinity cause calcium carbonate crystals to form on pool surfaces and equipment.
Total Alkalinity
In the swimming pool industry, total alkalinity is a measure of the dissolved carbonates and bicarbonates in water in parts per million (ppm).
High total alkalinity can be caused by the water supply to your pool.
When the total alkalinity is higher than 120ppm calcium scale can crystalize in your pool and equipment.
Calcium Hardness
Calcium Hardness is the measure of all calcium compounds dissolved in the pool water. In some areas the town water supply has a naturally high calcium hardness. Water sources from bores, dams and rivers can be high in minerals such as calcium. This results in faster mineral deposit formation in your pool. These water sources will require additional chemical treatment before the water is suitable for a swimming pool.
The recommended level of calcium is as low as possible to minimize any problems with calcium type deposits forming on the pool surfaces or in the salt water chlorinator cell.
The normal range for Calcium Hardness is 200 – 400 ppm
Total Dissolved Solids (TDS)
Total Dissolved Solids (TDS) is a measure of all materials dissolved in the pool water. This includes all pool chemicals, all contaminants, salt, carbonates & bicarbonates.
High TDS will cause calcium scale to accumulate in your pool even when the pool chemistry is correctly balanced.
Fresh water swimming pools should have a TDS up to 2000 ppm.
Salt water pools should have a TDS of 3000 to 6000 ppm. This is due to the dissolved pool salt in the water which accounts for 3000 to 4000ppm.
How to Remove Calcium Scale from a Pool
Remove Calcium Scale Without Draining the Pool
Brush the Pool Surfaces
Brush the walls, tile band and steps to remove calcium deposits. Wrap wet & dry sand paper around the brush and secure with waterproof plastic tape. Rub the sand paper over the walls to remove stubborn deposits.
Wet & Dry Sanding Block
Get in the pool and manually clean the surfaces. Use a wet & dry sanding block (or a pumice stone) to remove stubborn deposits. Keep the sanding block wet while rubbing the surface. This works well on flat surfaces like plaster and tiles but not on aggregate.
Drain the Pool to Remove Calcium Scale
When a pool has a lot of calcium scale the best way to clean it off the pool surfaces is to empty the pool to have easy access to the surfaces. You may not need to completely empty the pool depending on the location of the scale. If the scale is only around the waterline drain the water down from the tile band and clean the tile band. When scale is only affecting the steps drain down to expose the pool steps.
Read our article on How to Drain Water from a Swimming Pool
Acid Wash
One way to remove scale is to perform an acid wash on the pool surfaces. An acid wash is normally carried out when you empty the whole pool. However, if scale is only affecting the upper surfaces of the pool you may want to only drain half the water then acid wash the exposed surfaces.
Please ensure you wear eye protection, mask, gloves and covered clothing before handling hydrochloric acid.
Add 3 cups of water to a bucket then 1 cup of hydrochloric acid to the water. Brush the acid wash on to the scale which will bubble and fume while dissolving the scale.
Brush the scale away and wash the surface with fresh water.
Wet & Dry Sanding Block
When the pool is empty it’s easy to sand away scale. Use a wet & dry sanding block (or a pumice stone) to remove stubborn deposits. Keep the sanding block wet while rubbing the surface. This works well on flat surfaces like plaster and tiles but not on aggregate.
Angle Grinder & Cleaning Disk
I always use an angle grinder with a soft, low abrasive fibreglass flap disk to clean calcium scale from a pool. The disk is a soft, ribbed material for polishing fibreglass but works very well on plaster and tiles. This method will also polish plaster and remove most surface stains.
Purchase a grinder and disks from a good hardware store. Always keep the disk wet and only apply very light pressure to remove the scale. Start with a very fine disk first and move to a more course disk if required.
Spray the Scale with Scale Remover
Purchase a chemical spray that dissolves and removes calcium deposits. Spray directly onto the calcium deposits to clean calcium scale from a pool. After the scale has dissolved wash down with fresh water.
How to Prevent Calcium Scale in a Pool
As with most things in life the prevention is easier than the cure. It is far easier to prevent calcium deposits forming in the pool than it is to remove it. The scale is a very hard and pale crystalline substance which bonds to surfaces like glue. If you don’t keep it under control you will need to empty the pool and acid wash the pool surface and equipment.
Follow the recommendations below and hopefully you will never have to deal with scale in your pool.
Regularly Test the Pool Water
Purchase test strips or a test kit that includes tests for total alkalinity, calcium hardness and total dissolved solids. Test the water every week and immediately after heavy rain.
When the pool chemistry is not balanced correct it as soon as possible to prevent it getting out of control. Unbalanced pool water will cause calcium scale to begin to accumulate in the pool and equipment.
Regularly Clean the Pool
Clean your pool every week.
Begin by brushing the walls, tile band and steps to prevent calcium deposits forming. Wrap wet & dry sand paper around the brush to help remove stubborn deposits. Use a pumice stone or a wet & dry sanding block to rub over the ceramic tile band. Always wet the pumice or sanding block to prevent scratching the pool surfaces.
Vacuum your pool after brushing to remove loose calcium crystals that have fallen to the bottom.
Reduce the Total Alkalinity in the Pool Water
If the pH level is normal use sodium bisulphate to lower the total alkalinity as this will not adversely change the pH. Carefully read the instructions on the container to use the correct dosage for the volume of water in your pool.
If the pH level is higher than normal add hydrochloric acid or muriatic acid to the pool. Add one cup of acid to a bucket of water and pour evenly around the pool.
Run the pump for a while to mix in the chemicals and circulate the water around the pool.
Test the pool water every day and add more chemicals as required to reduce the total alkalinity into the desired range.
Note: If you need to adjust both pH and Total Alkalinity, always adjust the Total Alkalinity level first as the pH may change.
Read our article on How to Lower the Pool Alkalinity Level
Reduce the Calcium Hardness in the Pool Water
The easiest way to reduce the level of calcium in the pool is to drain or partially drain your pool and refill with fresh water.
Test your water supply by filling a bucket from your tap and dip in a test strip that measures calcium hardness. If the water supply is too hard you will need to add a chemical to your pool to lower the calcium hardness.
Note: Do not use calcium hypochlorite (dry granular chlorine) to raise the free chlorine level in your pool. This chemical will increase the calcium hardness of the water.
Reduce the Total Dissolved Solids in the Pool Water
There are no chemical products that will lower the level of total dissolved solids (TDS) in the pool water. The only way to reduce the level of TDS is to drain or partially drain your pool and refill with fresh water.
TDS is a common problem with all swimming pools, spas and hot tubs. Every swimming pool should be drained, cleaned and refilled with fresh water every 5 years.
Add Scale Remover to the Pool Water
Purchase scale remover chemical and add it to the pool water. The scale will dissolve away after a few weeks. You may need to apply a second dose after two weeks. Ensure you read the instructions on the container.
Conclusion
Calcium carbonate deposits are best avoided by maintaining correctly balanced pool water with low total alkalinity and low total dissolved solids. Test your pool water every week and take action as soon as the pH or total alkalinity is too high.
Once calcium deposits have formed in your pool re-balance the pool water chemistry and remove the calcium scale from the pool with the above methods.
Add scale remover chemical to the water to prevent the problem recurring.