diff --git a/exercises/exercise-biomineralization/README.md b/exercises/exercise-biomineralization/README.md
index 90a6886f036fbd47064be85056f27f441640b149..a5909d93082d2506d32d69a9ee09f79cea09c5d0 100644
--- a/exercises/exercise-biomineralization/README.md
+++ b/exercises/exercise-biomineralization/README.md
@@ -37,7 +37,7 @@ There are two types of solid components. Reactive and inert. For each reactive c
 
 ### 2. Implement a chemical equation
 
-In the following the basic steps required to set the new chemical equation are outlined. Here, this is done in the __chemistry__ folder in the prepared file: `simplebiominreactions.hh` starting in line 96.
+In the following the basic steps required to set the new chemical equation are outlined. Here, this is done in the __chemistry__ folder in the prepared file: `simplebiominreactions.hh` within the function reactionSource().
 Please be aware, that the chemistry file already provides some convenience functions (e.g. ``moleFracToMolality()``).
 
 __Task__
@@ -64,15 +64,17 @@ which is:
 
 Calcium ion + Urea + 2 Water → 2 Ammonium ions + Calcite
 
+Note that since the chemistry is simplified for this dumux-course example, the component Ammonium is neglected and you thus cannot set its source term, even though it is produced in the real reaction.
+
 ### 3. Make use of your newly created chemical equation
 
-To enable your newly created chemical equation, the chemistry file has to be included in your problem file. This has to be done in line 35:
+To enable your newly created chemical equation, the chemistry file has to be included in your problem file.
 
 ```c++
 #include "chemistry/simplebiominreactions.hh"   // chemical reactions
 ```
 
-Additionally the TypeTag of your chemistry file needs to be set in the problem file (line 125):
+Additionally the TypeTag of your chemistry file needs to be set in the problem file, within the class ExerciseFourBioMinProblem:
 
 ```c++
 using Chemistry = typename Dumux::SimpleBiominReactions<NumEqVector, VolumeVariables>;
@@ -80,7 +82,7 @@ using Chemistry = typename Dumux::SimpleBiominReactions<NumEqVector, VolumeVaria
 
 __Task__
 
-Now the source/sink term can be updated in the problem file. You find it in line 343. You can access the newly created chemistry file and call the reactionSource()-function from it. Make sure to call the reactionSource()-function with the correct arguments. Return the updated source terms in the end.
+Now the source/sink term can be updated in the problem file in its function source(). You can access the newly created chemistry file and call the reactionSource()-function from it. Make sure to call the chemistry.reactionSource()-function with the correct arguments. Return the updated source terms in the end.
 The volume variables can be set using the element volume variables and the sub control volume:
 
 ```c++
diff --git a/exercises/exercise-biomineralization/biominproblem.hh b/exercises/exercise-biomineralization/biominproblem.hh
index 20d0790b88d77a7958e45cbc185edcb8ba6230e7..ab0a787a766dc45440aef3740a0b43cce6b794d9 100644
--- a/exercises/exercise-biomineralization/biominproblem.hh
+++ b/exercises/exercise-biomineralization/biominproblem.hh
@@ -281,7 +281,7 @@ public:
         // Set values for Ca + urea injection above aquitard.
         // Use negative values for injection.
         if(globalPos[0] < eps_
-           && globalPos[1] > 11.0 + eps_
+           && globalPos[1] > 11.0 - eps_
            && globalPos[1] < 12.0 + eps_
            && time_ < injBioTime_)
         {