Despite the fact that pool water appears to be crystal clear and clean, it doesn’t necessarily mean that its chemistry is balanced. One of the factors that pool owners tend to ignore is water hardness. When the calcium level in your pool is too high or too low, it will damage your pool surfaces, water, pipe lines, and even the equipment in the pool. Learning about your pool water hardness and how to balance it will guarantee that your pool will be safe for use without incurring high expenses for repairs.
What Is Pool Water Hardness?
Hardness of water in pools is described as the presence of minerals within water, which include calcium and magnesium. The hardness of water is significant when it comes to pool management since it affects the behavior of water when it comes into contact with plaster, concrete, tiles, and metal.
Water with calcium at a low concentration has a tendency to leach out calcium from plaster. If the level is too high, there will be a tendency for calcium to deposit on pool walls, tiles, filters, and heaters, thus forming white hard deposits.
What Is Calcium Hardness?
Calcium hardness is the term used for the measure of calcium that is dissolved in the pool water. Calcium hardness is normally measured in parts per million (ppm).
Calcium is an organic mineral present in many forms of water sources. Calcium will be introduced in the pool through the use of tap water, pool chemicals, and when adding water for the evaporation that occurs in the pool.
Calcium hardness is different from pH and total alkalinity. They have different functions but are related in terms of maintaining balanced pool water.
What Is the Ideal Pool Water Hardness Level?
For some swimming pools, 200 to 400 ppm calcium hardness would be a good starting point for a target range. But the right target range depends on what type of finish you have on your pool and what the temperature is.
Concrete or plaster swimming pools will typically require more calcium than vinyl or fiberglass swimming pools. Check with your manufacturer’s specifications first.
Here is a table of reference for pool water hardness and the associated water chemistry.
| Water Chemistry Measurement | Common Target Range | Why It Matters |
|---|---|---|
| Calcium hardness | 200–400 ppm | Helps protect pool surfaces and equipment |
| pH | 7.4–7.6 | Controls how acidic or basic the water is |
| Total alkalinity | 80–120 ppm | Helps keep pH stable |
| Free chlorine | 1–3 ppm | Helps control bacteria and algae |
These are general guidelines for residential pools, not universal limits. Your pool surface, sanitizer system, and manufacturer instructions may require different targets.
Why Does the Ideal Level Matter?
Maintaining calcium hardness levels in the recommended range can help avoid any issues with surface problems or scaling.
However, the hardness of calcium does not dictate whether water is balanced. The pH level, alkalinity, and temperature all affect the solubility of calcium. A pool expert can evaluate these measurements together when there continue to be problems with scale formation.
What Happens When Pool Water Hardness Is Too Low?
Low levels of calcium hardness do not have any visible consequences initially, but pool owners tend to ignore that. However, if the level of calcium stays low for a long time, the water becomes aggressive toward all the elements with calcium content.
Etching of Pool Plaster and Concrete
When there is insufficient calcium in the water, it tends to take the minerals out of plaster and concrete. This results in damage to the surface of the pool, such as etching and pitting.
Risk to Metal Parts
Calcium hardness deficiency can play its role in creating a corrosive water balance if there are also low pH and low alkalinity levels in the water. Metal components, such as metal fittings, ladders, and equipment parts, may get affected by the presence of the discussed factors.
It should be understood that calcium hardness is just one factor causing the issue; there can also be other chemical factors, including low pH, that lead to corrosion.
How Can You Identify Low Calcium Hardness?
Low calcium hardness cannot be diagnosed simply by looking at water. Water balance problems can be an indication if etching is present, along with rough plastering or even deteriorated grout.
However, if any of these signs are seen, then do not add any chemicals to the water without testing it first.
What Happens When Pool Water Hardness Is Too High?
A high level of calcium hardness usually occurs when the source of the water is highly mineralized. Water evaporation from the pool may result in an increase in the amount of calcium because water evaporates while leaving the minerals intact.
Calcium Deposits on Pool Surfaces
Calcium that comes out of water will deposit some white or grey spots on tile, steps, water line and other areas of the pool. The deposits are often referred to as calcium scales.
The deposits may make the surfaces look dirty despite cleaning. The deposits may be so firmly stuck that it will require special cleaning services to remove them.
The Water of the Pool Becomes Cloudy
Calcium is one of the minerals that may cause cloudiness of the pool water, particularly in cases where pH and alkalinity levels are high. Fine mineral particles tend to appear and stay in suspension.
It should be noted though that cloudiness may also be caused by other reasons. For example, by poor filtration or algae.
Heat Sources and Filtration Equipment May be Affected
Calcium scale is a possibility for collecting on heater elements, pipes, filtration equipment and salt water chlorination cell components. Such scaling can impede water flow and inhibit heat exchange.
Over time, this scaling could add stress to the equipment causing additional servicing to be required. Properly balanced water can minimize this potential issue.
How to Test Pool Water Hardness
Testing is the first step to rectify any calcium hardness. It is risky to estimate the mineral content in the pool and use chemical treatments according to it because it can aggravate the issue.
Use of Pool Water Testing Kits
The appropriate pool test kits can help you know the existing calcium hardness in the pool water. Some tests employ liquid reagents whereas other tests involve the use of test strips or electronic testing equipment.
Make sure to follow the manufacturer’s directions and ascertain whether your tests measure the calcium hardness and not total hardness. The total hardness comprises both calcium and magnesium, thus they differ from each other.
Testing When Required
Test your pool water periodically during your pool maintenance activities. It makes sense to do it after the addition of a large volume of water in the pool, evaporation of large quantities of water or appearance of scale.
In cases of warm climate such as Florida, evaporation of water becomes more frequent leading to the changes in the concentration of the dissolved minerals in the water.
How to Balance Pool Water Hardness
When you find out the amount of calcium hardness in your pool, you will then know whether to raise or lower it. The technique used will depend on these factors: measurement, pool size, surface type, and other water chemistry measurements.
Step 1: Testing Your Pool’s Water Balance
Before adding anything to your pool, it is necessary to test calcium hardness, pH levels, and total alkalinity. Identify the material used for the pool surface and instructions for chemical usage.
If a lot of the readings are way off from the recommended range, then it is better not to attempt fixing them all at once.
Step 2: Increase Pool Calcium Hardness
If the calcium hardness level in your pool is too low, you need to increase the level using a pool calcium increaser with calcium chloride.
First of all, determine the necessary dose of the product based on the amount of water in your swimming pool and on the results of your testing. After that, add the substance following the manufacturer’s recommendations and circulate the water for the appropriate period.
Avoid adding an extra dose of the chemical to shorten the period. This will increase the calcium level above the recommended levels.
Step 3: Reducing High Calcium Hardness
It can be somewhat harder to reduce high calcium hardness, as common pool chemicals will not simply eliminate calcium from water.
One solution is to partially drain the pool and fill it up with new water, which has lower calcium hardness. But first test the new water – if it is hard water, then dilution will not bring much change.
The procedure should be thought through thoroughly, as there are cases when it is dangerous to drain the pool due to groundwater conditions, pool structure, and other factors. You can always turn to a pool professional to check everything.
There are special pool treatments that can be used to control scale/mineral accumulation, but they don’t necessarily decrease the calcium level in water. Be sure what a treatment does before choosing it.
Step 4: Check the Water Again after Treatment
When you have made a correction to the water, make sure to run your circulation system for the time suggested by the manufacturer of the chemical. Test the calcium hardness and recheck the pH and alkalinity levels.
The chemical composition of the water may change while circulating and mixing with the other chemicals. That is why retesting becomes necessary.
What Causes Pool Water Hardness to Change?
Hardness in pool water does not always maintain a constant level; several factors may cause a rise or fall in the calcium concentration in the pool.
Evaporation and Water Replacement
During warm seasons, water will be evaporating from the pool, while most of the dissolved minerals will be left behind. With top-ups of water in the pool, these minerals will contribute to the existing hardness level.
When the source water has a high concentration of calcium, top-ups of water will lead to increased hardness.
Chemical Composition of Pool and Source Water
There are certain chemicals that have calcium in their composition. Calcium hypochlorite is an example of such chemicals – this is a chlorinated sanitizer which has calcium in its composition as well.
Water in which a pool is being filled may also be responsible for calcium hardness increase.
Bad Water Balance as a Whole
There is a relationship between calcium hardness, pH, alkalinity, and temperature. Thus, even if the amount of calcium in the water is within acceptable limits, other factors may create an imbalance and result in scale formation and corrosion.
This is why water testing is more efficient than testing for calcium only.
How to Prevent Pool Water Hardness Problems
The simplest way to control calcium hardness is to measure it before the situation becomes critical. Take measurements regularly and especially in cases of extensive usage or rapid evaporation.
Maintain the records for calcium hardness, pH levels, and alkalinity. Test the water that will be used for topping up and never use calcium additives regardless of how they affect the balance.
Clean small amounts of deposit, ensure good water circulation and examine the condition of the pool itself. In case when calcium hardness increases and scale formation occurs frequently, professional testing may reveal the reason.
Maintenance of this kind is especially important for year-round pools.
Conclusion
It is imperative that you make sure the water hardness in the pool is at its optimal level. Not only will it protect the pool from getting any kind of damage, but also it will prevent the equipment from getting damaged because of calcium scaling.
Any proper testing of water and its chemistry can prevent this problem. In case you find that your levels stay out of the recommended range or that there are repeated occurrences of calcium deposits despite all efforts on your part, seek help from a professional to determine the reason and choose the right solution.
In case you need help with the testing and balancing of the pool water, take a look at the pool water testing and maintenance service offered by Gator Pool Services.