Pool Water Balance: pH, Alkalinity, Hardness, and Chlorine

Maintaining the correct pool water balance is not just a whim, but a key condition for the health of swimmers, the longevity of equipment, and crystal-clear water. Ignoring these parameters leads to skin and eye irritation, corrosion or scale formation on the walls, and reduces the effectiveness of disinfectants. Regular monitoring and timely adjustment are the keys to comfortable and safe swimming.

Why Water Balance Matters?

Pool water balance is a complex state where key chemical indicators are within optimal limits. Disturbing this balance can lead to a number of problems:

• For health: Too low or too high pH levels cause irritation of the mucous membranes of the eyes and skin, making swimming unpleasant and even dangerous. Insufficient chlorine leads to the proliferation of bacteria and algae.
• For equipment: Incorrect pH or high water hardness can cause corrosion of metal pool parts (pumps, heaters) or, conversely, the formation of limescale on filters, pipes, and walls, which significantly shortens the equipment's lifespan.
• For water quality: Water can become cloudy, acquire an unpleasant odor, or change color, despite regular filtration. The effectiveness of chlorine as a disinfectant sharply decreases with incorrect pH levels, requiring more chemical consumption.

Key Parameters and Their Optimal Ranges

To maintain a healthy pool, it is necessary to regularly check and adjust several key parameters:

pH Level (Hydrogen Potential)

pH is a measure of the acidity or alkalinity of water. The ideal range for pool water is 7.2 to 7.6. This value is as close as possible to the pH of human tears, ensuring comfort for the eyes and skin.

• Low pH (less than 7.2): Water becomes acidic, causes corrosion of metal parts, damages pool finishes (tiles, liner), causes eye and skin irritation, and rapidly consumes chlorine.
• High pH (more than 7.6): Water becomes alkaline, leading to limescale formation, reducing chlorine effectiveness, making the water cloudy, and potentially causing irritation.

Correction: To increase pH, use soda ash (sodium carbonate); to decrease it, use sodium bisulfate or muriatic acid.

Total Alkalinity (TA)

Total alkalinity is the water's ability to resist changes in pH. It acts as a buffer, preventing sharp pH fluctuations. The ideal TA range is 80 to 120 parts per million (ppm).

• Low TA (less than 80 ppm): Water pH becomes unstable, difficult to adjust, and can change sharply from minor factors (rain, water addition, chemical use). This can also lead to corrosion.
• High TA (more than 120 ppm): Water pH becomes too stable and difficult to change. This can lead to cloudy water and limescale formation.

Correction: To increase TA, use sodium bicarbonate (baking soda). To decrease it, use sodium bisulfate or muriatic acid, but do so slowly and gradually.

Water Hardness (Calcium Hardness)

Water hardness indicates the concentration of dissolved minerals, primarily calcium and magnesium. The optimal range for pool calcium hardness is 180 to 220 ppm.

• Low hardness (less than 180 ppm): Water becomes "soft" and aggressive, it starts to "leach" minerals from the pool finish (concrete, plaster), causing its deterioration and corrosion of metal parts.
• High hardness (more than 220 ppm): Leads to limescale formation on walls, equipment, and filters, reducing their effectiveness and requiring frequent cleaning. It can also cause cloudy water.

Correction: To increase hardness, use calcium chloride. Decreasing hardness usually requires partial water replacement or the use of special agents — flocculants.

Free Chlorine (FC)

Free chlorine is the active form of chlorine that disinfects water by destroying bacteria, viruses, and algae. The ideal free chlorine level is 1 to 3 ppm.

• Low FC (less than 1 ppm): Insufficient disinfection, leading to algae and bacteria growth, water becomes green or cloudy.
• High FC (more than 3 ppm): Can cause a strong chlorine odor, irritation of eyes, skin, and respiratory tract. It can also damage pool finishes and bleach swimwear.

Correction: To increase FC, use chlorine-containing preparations (liquid chlorine, granules, tablets). To decrease it, use sodium thiosulfate or simply wait for the chlorine to break down under UV rays or with active pool use.

How Often to Test and With What?

Regular testing is the key to stable balance:

1. Free Chlorine and pH: It is advisable to check daily or at least 2-3 times a week, especially with active pool use or after rain.
2. Total Alkalinity and Hardness: These parameters are more stable and require checking once a week or once every two weeks.

Testing tools:

• Test strips: The simplest and fastest method. They are dipped in water for a few seconds and compared to a color scale. Suitable for quick daily checks.
• Liquid test kits (photometers): More accurate, they use reagents that change the water's color. They take a little more time but provide more reliable results. Ideal for weekly checks.

Correction Procedure

When adjusting water parameters, it is important to follow a specific sequence, as some indicators affect each other:

1. Testing: First, measure all four key parameters: pH, total alkalinity, hardness, and free chlorine.
2. Total Alkalinity (TA) Correction: If TA is outside the 80-120 ppm range, start by adjusting it. This is the basis of the water's buffer system, and only after its stabilization can you proceed to pH. After adding chemicals, allow the water to circulate for at least 4-6 hours, then re-measure TA.
3. pH Correction: After TA stabilization, proceed to adjust pH (ideal 7.2-7.6). Again, allow the water time to circulate (4-6 hours) and repeat the test.
4. Hardness Correction: If water hardness is too low (less than 180 ppm), add calcium chloride. If it's high, consider partial water replacement. Hardness correction is rarely needed frequently.
5. Free Chlorine Correction: Finally, bring the free chlorine level to normal (1-3 ppm). If you have adjusted pH and TA, chlorine effectiveness will be maximal.

Important: Add chemicals in small portions, distributing them evenly over the water surface, and never mix different chemicals directly. Always read manufacturer instructions and use protective equipment.

Common Pool Owner Mistakes

Even experienced pool owners sometimes make mistakes that lead to water problems:

• Ignoring regular testing: Many owners check the water only when it already looks bad. By this point, restoring balance is much more difficult and expensive. For example, a common mistake is not checking chlorine after active pool use, which leads to algae growth within 1-2 days.
• Incorrect order of chemical addition: As mentioned above, sequence is important. Correcting pH before TA often leads to pH