{"id":1619,"date":"2026-02-16T12:12:19","date_gmt":"2026-02-16T12:12:19","guid":{"rendered":"https:\/\/info.piscinasyspas.com\/guides\/water-and-maintenance\/water-chemistry\/"},"modified":"2026-04-14T12:19:33","modified_gmt":"2026-04-14T12:19:33","slug":"water-chemistry","status":"publish","type":"page","link":"https:\/\/info.piscinasyspas.com\/en\/guides\/water-and-maintenance\/water-chemistry\/","title":{"rendered":"Water chemistry"},"content":{"rendered":"

<\/div>

Water chemistry<\/h1><\/div>

pH, alkalinity, hardness, TDS, and cyanuric acid explained<\/p><\/h3><\/div><\/div><\/div><\/div><\/div><\/div><\/div><\/div>

Introduction<\/h2><\/div>

Water chemical balance<\/strong> refers to the state in which key parameters\u2014such as pH, alkalinity, and hardness\u2014are within appropriate and stable ranges. Within water and maintenance guides<\/a>, understanding these parameters is essential to maintaining system stability. <\/p>\n

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

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<\/strong> and the durability of the installation<\/strong>.<\/p>\n<\/div>

pH: a central parameter<\/h2><\/div>

What is pH?<\/h3>\n

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

Why its important<\/h3>\n

pH directly affects bather comfort<\/strong>, as values that are too low can cause irritation and values that are too high can create a rough water feel.<\/p>\n

It also has a clear impact on corrosion and scaling<\/strong>. A low pH promotes metal corrosion and surface deterioration, while a high pH increases the likelihood of limescale formation. <\/p>\n

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<\/a>. <\/p>\n

Recommended range in pools and spas<\/h3>\n

In residential pools and spas, the commonly recommended range is between 7.2 and 7.6<\/strong>. Staying within this range promotes system stability and proper water balance.<\/p>\n<\/div>

Total alcalinity<\/h2><\/div>

What is alcalinity<\/h3>\n

Total alkalinity<\/strong> measures the water\u2019s ability to neutralize acids, acting as a buffer system<\/strong>. In practice, it represents the concentration of bicarbonates and other compounds that help maintain chemical stability. <\/p>\n

Relation to pH<\/h3>\n

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

Consequences of incorrect values<\/h3>\n

Una alcalinidad demasiado baja puede provocar inestabilidad del pH<\/strong>, con oscilaciones r\u00e1pidas y dif\u00edciles de controlar. Por el contrario, una alcalinidad elevada puede favorecer una tendencia incrustante<\/strong> y dificultar la correcci\u00f3n del pH. <\/p>\n

Maintaining alkalinity within the recommended range helps prevent both aggressive water and the formation of limescale deposits.<\/p>\n<\/div>

Calcium hardness<\/h2><\/div>

What is hardness?<\/h3>\n

Calcium hardness<\/strong> indicates the concentration of dissolved calcium<\/strong> in the water. This mineral is one of the main factors influencing whether the water behaves as scaling or corrosive within the installation. <\/p>\n

Scaling risk<\/h3>\n

When hardness is high\u2014especially combined with a high pH\u2014calcium carbonate can precipitate<\/strong>. This results in white deposits on walls, the waterline, heat exchangers, and other equipment. <\/p>\n

Corrosive water risk<\/h3>\n

If hardness is too low, the water can become aggressive<\/strong> and tend to dissolve minerals from surfaces. This promotes corrosion and material deterioration<\/strong>, affecting both finishes and metal components.<\/p>\n<\/div>

Cyanuric acid<\/h2><\/div>

What is cyanuric acid<\/h3>\n

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

Function in outdoor pools<\/h3>\n

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

Problems when it accumulates<\/h3>\n

When cyanuric acid accumulates excessively, it can reduce the actual effectiveness<\/strong> 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<\/strong>. <\/p>\n

Recommended guideline values<\/h3>\n

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

TDS (Total Dissolved Solids)<\/h2><\/div>

What is TDS<\/h3>\n

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

How it accumulates<\/h3>\n

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

Whes does it become a problem<\/h3>\n

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

Parameter interactions<\/h2><\/div>

Overall balance<\/h3>\n

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

When the balance is not appropriate, the water may show a scaling tendency<\/strong>, promoting the formation of limescale deposits, or a corrosive tendency<\/strong>, which affects surfaces and metal components.<\/p>\n

The concept of saturation<\/h3>\n

The concept of saturation describes the point at which water is balanced with respect to calcium<\/strong>, with no tendency to precipitate or dissolve minerals. <\/p>\n

Balanced water remains stable over time, whereas unbalanced water will tend to cause scaling or corrosion, even if the individual values appear acceptable.<\/p>\n<\/div>

How to measure properly<\/h2><\/div>

Test strips<\/h3>\n

Test strips<\/strong> 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. <\/p>\n

Liquid reagent tests<\/h3>\n

Liquid reagent kits<\/strong> 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. <\/p>\n

Photometers<\/h3>\n

Electronic photometers<\/strong> 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. <\/p>\n

Recommended frequency depending on the type of installation<\/h3>\n

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<\/strong> are advisable, especially after periods of intensive use.<\/p>\n<\/div>

Common errors<\/h2><\/div>

Adjust pH without checking alcalinity<\/h3>\n

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

Ignoring cyanuric acid in outdoor pools<\/h3>\n

In outdoor pools, failing to control cyanuric acid<\/strong> can lead to a loss of the disinfectant\u2019s real effectiveness. Its gradual accumulation reduces sanitizing capacity, even when chlorine levels appear correct. <\/p>\n

Not take into account TDS buildup<\/h3>\n

The accumulation of total dissolved solids<\/strong> 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. <\/p>\n

Correcting parameters without a complete diagnosis<\/h3>\n

Applying products without first performing a complete and systematic measurement<\/strong> of the parameters can worsen the imbalance. Diagnosis should always come before correction to avoid unnecessary interventions.<\/p>\n<\/div>

Conclusion<\/h2><\/div>

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

When water is unbalanced, disinfection effectiveness<\/strong> decreases and the risk of scaling or corrosion increases. Understanding these principles enables more efficient and preventive maintenance. <\/p>\n

common water issues in pools, spas, and swim spas<\/p>\n

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<\/a>.<\/p>\n<\/div>

Recommended value ranges<\/h2><\/div>
\n\n\n\n\n<\/p>\n\n<\/p>\n\n<\/p>\n\n\n<\/p>\n\n
<\/th>\nResidential pool<\/th>\nSpa<\/th>\nSwim spa<\/th>\n<\/tr>\n<\/thead>\n
pH<\/td>\n

<\/strong><\/p>\n

7.2 \u2013 7.6<\/td>\n7.2 \u2013 7.6 (very frequent monitoring)<\/td>\n7.2 \u2013 7.6<\/td>\n<\/tr>\n
Total alkalinity<\/td>\n

<\/strong><\/p>\n

80 \u2013 120 ppm<\/td>\n80 \u2013 120 ppm<\/td>\n80 \u2013 120 ppm<\/td>\n<\/tr>\n
Calcium hardness<\/td>\n

<\/strong><\/p>\n

200 \u2013 400 ppm<\/td>\n150 \u2013 250 ppm<\/td>\n150 \u2013 300 ppm<\/td>\n<\/tr>\n
Cyanuric acid (CYA)<\/strong><\/td>\n20 \u2013 50 ppm (outdoor)<\/td>\nNot recommended<\/td>\n0 \u2013 20 ppm (depending on the system)<\/td>\n<\/tr>\n
TDS<\/td>\n

<\/strong><\/p>\n

\u2264 1500 ppm above fill water<\/td>\nRenew before +1000\u20131500 ppm<\/td>\nFrequent monitoring; periodic water replacement<\/td>\n<\/tr>\n
Saturation Index (LSI)<\/td>\n-0.3 to +0.3<\/td>\n-0.2 to +0.2 (more critical)<\/td>\n-0.3 to +0.3<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>

Important notes:<\/strong><\/p>\n

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

    The Langelier Saturation Index (LSI)<\/strong> 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.<\/p>\n<\/div><\/div><\/div><\/div><\/div><\/p>\n","protected":false},"excerpt":{"rendered":"","protected":false},"author":1,"featured_media":0,"parent":1476,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"100-width.php","meta":{"footnotes":""},"class_list":["post-1619","page","type-page","status-publish","hentry"],"_links":{"self":[{"href":"https:\/\/info.piscinasyspas.com\/en\/wp-json\/wp\/v2\/pages\/1619","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/info.piscinasyspas.com\/en\/wp-json\/wp\/v2\/pages"}],"about":[{"href":"https:\/\/info.piscinasyspas.com\/en\/wp-json\/wp\/v2\/types\/page"}],"author":[{"embeddable":true,"href":"https:\/\/info.piscinasyspas.com\/en\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/info.piscinasyspas.com\/en\/wp-json\/wp\/v2\/comments?post=1619"}],"version-history":[{"count":2,"href":"https:\/\/info.piscinasyspas.com\/en\/wp-json\/wp\/v2\/pages\/1619\/revisions"}],"predecessor-version":[{"id":1621,"href":"https:\/\/info.piscinasyspas.com\/en\/wp-json\/wp\/v2\/pages\/1619\/revisions\/1621"}],"up":[{"embeddable":true,"href":"https:\/\/info.piscinasyspas.com\/en\/wp-json\/wp\/v2\/pages\/1476"}],"wp:attachment":[{"href":"https:\/\/info.piscinasyspas.com\/en\/wp-json\/wp\/v2\/media?parent=1619"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}