Water chemistry

Water chemical balance refers to the state in which key parameters—such as pH, alkalinity, and hardness—are within appropriate and stable ranges. Within water and maintenance guides, understanding these parameters is essential to maintaining system stability.

It is important to distinguish between water chemistry, which describes the internal characteristics of the water, and treatment systems, which act on it through disinfection and filtration. Water chemistry defines the environment in which these systems must operate.

When the water is not balanced, disinfectant effectiveness decreases and issues such as corrosion, scaling, or parameter instability can arise. For this reason, chemical balance directly affects both treatment performance and the durability of the installation.

What is pH?

pH is a measure that indicates the acidity or alkalinity of water on a scale from 0 to 14. Values below 7 indicate acidity, values above 7 indicate alkalinity, and 7 is considered neutral.

Why its important

pH directly affects bather comfort, as values that are too low can cause irritation and values that are too high can create a rough water feel.

It also has a clear impact on corrosion and scaling. A low pH promotes metal corrosion and surface deterioration, while a high pH increases the likelihood of limescale formation.

pH also has an indirect impact on disinfectant effectiveness, as it influences its ability to act. Even with correct product levels, an out-of-range pH can significantly reduce treatment effectiveness. The different disinfection systems are analyzed in more detail in the guide on chlorine, bromine, and alternative disinfection methods.

Recommended range in pools and spas

In residential pools and spas, the commonly recommended range is between 7.2 and 7.6. Staying within this range promotes system stability and proper water balance.

What is alcalinity

Total alkalinity measures the water’s ability to neutralize acids, acting as a buffer system. In practice, it represents the concentration of bicarbonates and other compounds that help maintain chemical stability.

Relation to pH

Alkalinity is closely related to pH, as it determines its stability against fluctuations. When alkalinity is within the proper range, pH changes more slowly and in a controlled manner in response to chemical additions or usage variations.

Consequences of incorrect values

Una alcalinidad demasiado baja puede provocar inestabilidad del pH, con oscilaciones rápidas y difíciles de controlar. Por el contrario, una alcalinidad elevada puede favorecer una tendencia incrustante y dificultar la corrección del pH.

Maintaining alkalinity within the recommended range helps prevent both aggressive water and the formation of limescale deposits.

What is hardness?

Calcium hardness indicates the concentration of dissolved calcium in the water. This mineral is one of the main factors influencing whether the water behaves as scaling or corrosive within the installation.

Scaling risk

When hardness is high—especially combined with a high pH—calcium carbonate can precipitate. This results in white deposits on walls, the waterline, heat exchangers, and other equipment.

Corrosive water risk

If hardness is too low, the water can become aggressive and tend to dissolve minerals from surfaces. This promotes corrosion and material deterioration, affecting both finishes and metal components.

What is cyanuric acid

Cyanuric acid is a compound used as a chlorine stabilizer in pools, especially when stabilized chlorine products are used. Its main function is to protect the disinfectant from degradation caused by sunlight.

Function in outdoor pools

In pools exposed to sunlight, cyanuric acid provides protection against UV radiation, reducing the rate at which chlorine breaks down. This results in greater disinfectant stability and reduced daily consumption.

Problems when it accumulates

When cyanuric acid accumulates excessively, it can reduce the actual effectiveness of the disinfectant, as part of the chlorine becomes chemically bound. In such cases, the only effective way to lower its concentration is usually partial water replacement.

Recommended guideline values

In residential outdoor pools, cyanuric acid should be kept within a controlled range to balance protection and effectiveness. In spas, its use is generally not recommended or is kept at very low levels due to the reduced water volume and higher temperature.

What is TDS

Total dissolved solids (TDS) represent the sum of salts, chemicals, and organic residues that remain dissolved in the water. They include both components added for treatment and substances introduced through use.

How it accumulates

TDS increase progressively due to evaporation and refilling, as water evaporates but the solids remain. They also rise with continuous use, which introduces new substances and by-products into the system.

Whes does it become a problem

When TDS reach high levels, an increase in water conductivity and greater difficulty in maintaining stable parameters can be observed. Under these conditions, chemical stability may be compromised, often requiring partial or complete water replacement.

Overall balance

Water behavior does not depend on a single isolated value, but on the relationship between pH, alkalinity, and calcium hardness. These three parameters interact and determine whether the water remains stable or tends to drift.

When the balance is not appropriate, the water may show a scaling tendency, promoting the formation of limescale deposits, or a corrosive tendency, which affects surfaces and metal components.

The concept of saturation

The concept of saturation describes the point at which water is balanced with respect to calcium, with no tendency to precipitate or dissolve minerals.

Balanced water remains stable over time, whereas unbalanced water will tend to cause scaling or corrosion, even if the individual values appear acceptable.

Test strips

Test strips allow a quick, indicative measurement of several parameters simultaneously. They are practical for frequent checks, although their accuracy may be limited and depends on correct color interpretation.

Liquid reagent tests

Liquid reagent kits offer greater reliability than test strips and allow more precise measurement of pH, chlorine, bromine, and other basic parameters. They require a bit more time and care when reading the results.

Photometers

Electronic photometers provide more accurate measurements through digital analysis of the sample. They are especially useful in high-use installations or when more technical and documented control is required.

Recommended frequency depending on the type of installation

In residential pools, it is recommended to measure basic parameters several times per week during the usage season. In spas and swim spas, due to their lower volume and higher temperature, more frequent checks are advisable, especially after periods of intensive use.

Adjust pH without checking alcalinity

Adjusting pH without first checking total alkalinity can lead to constant fluctuations and difficulty stabilizing the water. If alkalinity is not within range, any pH adjustment will be temporary.

Ignoring cyanuric acid in outdoor pools

In outdoor pools, failing to control cyanuric acid can lead to a loss of the disinfectant’s real effectiveness. Its gradual accumulation reduces sanitizing capacity, even when chlorine levels appear correct.

Not take into account TDS buildup

The accumulation of total dissolved solids is a gradual process that often goes unnoticed. When not controlled, it can make it harder to maintain chemical balance and affect the overall stability of the water.

Correcting parameters without a complete diagnosis

Applying products without first performing a complete and systematic measurement of the parameters can worsen the imbalance. Diagnosis should always come before correction to avoid unnecessary interventions.

Water chemistry forms the foundation on which all treatment systems rely. Without a proper balance of pH, alkalinity, hardness, and other parameters, water stability is compromised.

When water is unbalanced, disinfection effectiveness decreases and the risk of scaling or corrosion increases. Understanding these principles enables more efficient and preventive maintenance.

common water issues in pools, spas, and swim spas

In technical spa and swim spa installations, it can also be useful to review real examples of filtration, control, and water treatment systems used in professional equipment, such as those found at Aqaspas.

Important notes:

• Ranges may vary slightly depending on local regulations.
• In spas, the frequency of monitoring is more critical than the range itself.
• In swim spas, chemical behavior is intermediate between that of a pool and a spa.

The Langelier Saturation Index (LSI) makes it possible to assess whether the water has a scaling tendency (positive LSI) or a corrosive tendency (negative LSI). Keeping the index close to zero indicates proper balance between pH, alkalinity, hardness, and temperature.