Technical definition
Potassium is a measurement of the concentration of dissolved potassium ions (K⁺) present in the heating system water, expressed in milligrams per litre (mg/L).
Potassium occurs naturally in water as a dissolved positively charged ion, although its concentration varies according to the water source and local geology. It can also enter heating-system water through chemical treatment products, cleaning chemicals, filling water or other sources of contamination. Potassium is one of the dissolved cations that contributes to the overall ionic composition of water.
Within a heating system, potassium is primarily useful as an indicator of water chemistry and possible chemical additions. Unlike calcium and magnesium, potassium is not normally considered a hardness-forming ion and does not directly create conventional limescale.
Fernox laboratory data currently specifies a recommended potassium concentration of less than 125 mg/L for the water-analysis parameter.
Simplified definition
Potassium is a dissolved mineral that may be naturally present in the filling water or introduced through chemical treatments or contamination.
It does not normally cause limescale itself, but measuring it helps identify changes in the system water and can provide useful information about the system's water source, treatment history and overall chemical condition.
Potassium is useful because an elevated or unexpected concentration can indicate that the chemical composition of the heating system water has changed.
An abnormal Potassium result may indicate:
Naturally elevated potassium in the original filling water.
Introduction of a potassium-containing treatment or cleaning chemical.
Residual chemicals remaining following system cleaning or maintenance.
Contamination from another water or chemical source.
Changes in the system following draining, flushing or refilling.
Increasing concentrations of dissolved salts within the circulating water.
Water chemistry that differs significantly from the original filling water.
Because potassium exists in water as a dissolved ion, potassium-containing salts contribute to the overall dissolved ionic content of the system water and therefore contribute to conductivity. However, the significance of an elevated potassium result depends heavily on the chemical compound from which the potassium originates.
For example, potassium may be associated with compounds containing carbonate, hydroxide, chloride or other ions, each of which can influence heating-system water chemistry differently. It is therefore important not to interpret the potassium concentration without considering the other parameters present.
Potassium testing can help:
Establish a more complete chemical fingerprint of the system water.
Identify differences between the filling water and circulating system water.
Provide evidence of chemical additions or contamination.
Support investigation of unusual conductivity or alkalinity results.
Identify unexpected changes following cleaning, treatment or maintenance.
Confirm whether the water chemistry remains within the recommended Fernox range.
Fernox laboratory testing includes Potassium as a separate parameter and currently identifies <125 mg/L as the recommended level.
Potassium should therefore be considered alongside parameters such as Sodium, Conductivity, Chloride, M-Alkalinity, P-Alkalinity and treatment-related chemical indicators when assessing the overall chemical condition of heating-system water.
Potassium should not normally be assessed in isolation. A raised potassium concentration does not automatically mean that corrosion, scale or another system problem is occurring.
Unlike calcium and magnesium, potassium itself is not a conventional hardness-forming mineral. The potential significance of a high result depends on the substance with which the potassium is associated and the effect that substance has on the overall system-water chemistry.
For example, an elevated potassium result accompanied by a significant increase in conductivity, alkalinity, chloride or pH may provide more useful diagnostic information than the potassium concentration alone.
It is also helpful to compare the result with the original filling water and previous system-water results. A large increase in potassium after the system has been filled may indicate the introduction of a chemical product or another source of dissolved salts.
Fernox currently specifies a recommended Potassium concentration of less than 125 mg/L, so results above this level should be considered alongside the remaining laboratory parameters and the known treatment history of the system.
