diff -r b36d249512cc -r 19156b8b339f src/EditRecipeTab7.cpp
--- a/src/EditRecipeTab7.cpp	Mon Apr 25 12:53:36 2022 +0200
+++ b/src/EditRecipeTab7.cpp	Mon Apr 25 15:52:21 2022 +0200
@@ -396,7 +396,120 @@
     ui->wb_hco3Edit->setStyleSheet((bicarbonate > 250) ? "background-color: red":"background-color: green");
     ui->wb_caco3Edit->setStyleSheet((bicarbonate > 250) ? "background-color: red":"background-color: green");
 
-    // calcSparge();
+    calcSparge();
+}
+
+
+/*
+ * Based on the work of ajDeLange.
+ */
+void EditRecipe::calcSparge()
+{
+    double TargetpH = recipe->sparge_ph;
+    double Source_pH = recipe->w1_ph;
+    double Source_alkalinity = recipe->w1_total_alkalinity;
+
+    qDebug() << "calcSparge()";
+
+    const QSignalBlocker blocker1(ui->sp_sourceEdit);
+
+    // Select watersource or fallback to the first source.
+    if (recipe->sparge_source == 1) { // Source 2
+	if (recipe->w2_ph > 0.0 && recipe->w2_amount > 0) {
+	    Source_pH = recipe->w2_ph;
+	    Source_alkalinity = recipe->w2_total_alkalinity;
+	} else {
+	    recipe->sparge_source = 0; // Source 1
+	    ui->sp_sourceEdit->setCurrentIndex(0);
+	}
+    } else if (recipe->sparge_source == 2) { // Mixed
+	if (recipe->w2_ph > 0.0 && recipe->w2_amount > 0) {
+	    Source_pH = recipe->wg_ph;
+	    Source_alkalinity = recipe->wg_total_alkalinity;
+	} else {
+	    recipe->sparge_source = 0; // Source 1
+            ui->sp_sourceEdit->setCurrentIndex(0);
+	}
+    }
+
+    // Step 1: Compute the mole fractions of carbonic (f1o), bicarbonate (f2o) and carbonate(f3o) at the water pH
+    double r1 = pow(10, Source_pH - 6.35);
+    double r2 = pow(10, Source_pH - 10.33);
+    double d = 1 + r1 + r1 * r2;
+    double f1 = 1 / d;
+    double f3 = r1 * r2 / d;
+
+    // Step 2. Compute the mole fractions at pH = 4.3 (the pH which defines alkalinity)
+    double r143 = pow(10, 4.3 - 6.35);
+    double r243 = pow(10, 4.3 - 10.33);
+    double d43 = 1 + r143 + r143 * r243;
+    double f143 = 1 / d43;
+    double f343 = r143 * r243 / d43;
+
+    // Step 4. Solve
+    //double Ct = (Source_alkalinity - 1000 * (pow(10, -4.3) - pow(10, -Source_pH))) / ((f143 - f1) + (f3 - f343));
+    double Ct = Source_alkalinity / 50 / ((f143 - f1) + (f3 - f343));
+
+    // Step 5. Compute mole fractions at desired pH
+    double r1g = pow(10, TargetpH - 6.35);
+    double r2g = pow(10, TargetpH - 10.33);
+    double dg = 1 + r1g + r1g * r2g;
+    double f1g = 1 / dg;
+    double f3g = r1g * r2g / dg;
+
+    // Step 6. Use these to compute the milliequivalents acid required per liter (mEq/L)
+    double Acid = Ct * ((f1g - f1) + (f3 - f3g)) + pow(10, -TargetpH) - pow(10, -Source_pH);  //mEq/l
+    Acid += 0.01;   // Add acid that would be required for distilled water.
+
+    //Step 8. Get the acid data.
+    int AT = recipe->sparge_acid_type;
+    if (AT < 0 || AT >= my_acids.size()) {
+	AT = 0;
+	recipe->sparge_acid_type = 0;
+	ui->sp_acidtypeEdit->setCurrentIndex(0);
+	recipe->sparge_acid_perc = my_acids[0].AcidPrc;
+	ui->sp_acidpercEdit->setValue(recipe->sparge_acid_perc);
+    }
+    double fract = Utils::CalcFrac(TargetpH, my_acids[AT].pK1, my_acids[AT].pK2, my_acids[AT].pK3);
+
+    // Step 9. Now divide the mEq required by the "fraction". This is the required number of moles of acid.
+    Acid /= fract;
+
+    // Step 10. Multiply by molecular weight of the acid
+    Acid *= my_acids[AT].MolWt; //mg
+
+    // Step 11. Divide by Specific Gravity and Percentage to get the final ml.
+    Acid = Acid / my_acids[AT].AcidSG / (recipe->sparge_acid_perc / 100); //ml
+    Acid *= recipe->sparge_volume; //ml acid total
+    Acid = round(Acid * 100.0) / 100.0;
+    recipe->sparge_acid_amount = Acid / 1000;
+    ui->sp_acidvolEdit->setValue(Acid);
+}
+
+
+void EditRecipe::sp_source_changed(int val)
+{
+    recipe->sparge_source = val;
+    calcSparge();
+    is_changed();
+}
+
+
+void EditRecipe::sp_type_changed(int val)
+{
+    recipe->sparge_acid_type = val;
+    recipe->sparge_acid_perc = my_acids[val].AcidPrc;
+    ui->sp_acidpercEdit->setValue(recipe->sparge_acid_perc);
+    calcSparge();
+    is_changed();
+}
+
+
+void EditRecipe::sp_ph_changed(double val)
+{
+    recipe->sparge_ph = val;
+    calcSparge();
+    is_changed();
 }