Charge-Balance Adjustment

First Step:  Calculate Charge Balance Error

The first thing aqion does when you click the Start button is to calculate the charge-balance error (CBE) of the input water. The screenshot below shows the CBE of the example water “dump.sol”.


The output panel displays:

  • the CBE in percent
  • the sum of cations in meq/L
  • the sum of anions in meq/L

Now, the user has the possibility to re-adjust one chemical parameter in order to obtain complete charge balance. For this purpose you should select one of the following parameters from the corresponding pull-down list:1

•  pH value (default)
•  Ca  
•  Mg  
•  Na  
•  K  
•  SO4 [S(6)]
•  DIC [C(4)]
•  Cl  
•  NO3 [N(5)]
•  NH4 [N(-3)]
•  … etc.  

Note 1. The parameter list contains only those elements that are present in the actual input water (with a minimum concentration of 1 µmol/L). For example, if the input water does not contain Al, then Al is absent in the pull-down list.

Note 2. The button Details opens a guidance for charge-balance adjustment. It provides a hint which parameter, cation or anion, should be selected to improve the discrepancy.

Second Step:  Charge-Balance Adjustment


The example above has an error of 4.2%. If we select the parameter SO4 and click on next the right screenshot pops up. It tells us that sulfate is enhanced:2

   167.25 mM ⇒ 173.58 mM

The line below displays the amount added (as the difference of both values):

   ΔSO4 = 6.33 mM

A positive (negative) Δ-value signals addition (removal) of the element. In any case, the obtained solution is completely charge-balanced (and stored as Output 1).

In addition, aqion performs a second calculation (Output 2) to check whether minerals precipitate or not. In this case the equilibrium solution is supersaturated with the mineral barite (BaCO3), and when barite precipitates the pH changes from 2.81 to 2.84.


  1. The symbols in square braces represent the corresponding valence states

  2. In the line below the concentration unit can be switched between mg/L and mmol/L. 

[last modified: 2015-07-05]