What is it: The ion balance is an important tool for checking the plausibility of a comprehensive laboratory analysis and compares the electrical charge of the measured major ions in freshwater. Positively charged cations such as sodium, magnesium, calcium, potassium, strontium, lithium, iron, manganese and aluminium are compared with negatively charged anions such as chloride, sulfate, bromide, fluoride, nitrate, bicarbonate and orthophosphate.
A result close to 0 % indicates a balanced ratio. Positive values may indicate an excess of cations or a deficiency of anions, while negative values may indicate an excess of anions or a deficiency of cations. Deviations of up to ±5 % are considered inconspicuous, values between ±5 and ±8 % are already relatively rare and should at least be monitored. Shifts outside ±8 % must be investigated more closely.

Problems: A clearly shifted ion balance indicates that the measured major ions are no longer present in the expected ratio to one another. Possible causes include high organic loads, unbalanced dosing, unsuitable remineralisation or hardening agents, high nutrient inputs or long-term shifts caused by the supply system in use. Fertilisers, water conditioners, mineral salts and other additives as well as organic or ionic components that are not fully detected can also influence the result. In the freshwater ion balance, iron, manganese and aluminium are additionally taken into account as cations, among others, while measured orthophosphate is included as an anion. The ion balance therefore evaluates the water chemistry as a whole and by itself does not allow the exact cause to be determined.

Measures: Previous analysis trends, dosing quantities, source water, hardening and remineralisation agents, fertilisers and the supply system in use should also be checked. An abnormal ion balance should not be corrected by blindly adding individual salts. The most important and gentle countermeasure is a water change with suitable, high-quality and balanced freshwater, as this removes excess ions and brings the major ions back into a more balanced ratio. If the deviation persists despite regular water changes or lies outside ±8 %, a targeted search for the cause based on the individual values and their development over time is required.