diff --git a/test_problems/VCSnonideal/NaCl_equil/HMW_NaCl.xml b/test_problems/VCSnonideal/NaCl_equil/HMW_NaCl.xml
index eb8514cd3..eb5c93285 100644
--- a/test_problems/VCSnonideal/NaCl_equil/HMW_NaCl.xml
+++ b/test_problems/VCSnonideal/NaCl_equil/HMW_NaCl.xml
@@ -66,20 +66,20 @@
                 </binarySaltParameters>
 
                 <thetaAnion anion1="Cl-" anion2="OH-">
-                  <Theta> -0.05 </Theta>
+                  <theta> -0.05 </theta>
                 </thetaAnion>
 
                 <psiCommonCation cation="Na+" anion1="Cl-" anion2="OH-">
-                  <Theta> -0.05 </Theta>
+                  <theta> -0.05 </theta>
                   <Psi> -0.006 </Psi>
                 </psiCommonCation>
 
                 <thetaCation cation1="Na+" cation2="H+">
-                  <Theta> 0.036 </Theta>
+                  <theta> 0.036 </theta>
                 </thetaCation>
 
                 <psiCommonAnion anion="Cl-" cation1="Na+" cation2="H+">
-                  <Theta> 0.036 </Theta>
+                  <theta> 0.036 </theta>
                   <Psi> -0.004 </Psi>
                 </psiCommonAnion>
 
diff --git a/test_problems/cathermo/HMW_dupl_test/HMW_NaCl_sp1977_alt.xml b/test_problems/cathermo/HMW_dupl_test/HMW_NaCl_sp1977_alt.xml
index adaff9c71..abdbbb967 100644
--- a/test_problems/cathermo/HMW_dupl_test/HMW_NaCl_sp1977_alt.xml
+++ b/test_problems/cathermo/HMW_dupl_test/HMW_NaCl_sp1977_alt.xml
@@ -73,20 +73,20 @@
                 </binarySaltParameters>
 
                 <thetaAnion anion1="Cl-" anion2="OH-">
-                  <Theta> -0.05 </Theta>
+                  <theta> -0.05 </theta>
                 </thetaAnion>
 
                 <psiCommonCation cation="Na+" anion1="Cl-" anion2="OH-">
-                  <Theta> -0.05 </Theta>
+                  <theta> -0.05 </theta>
                   <Psi> -0.006 </Psi>
                 </psiCommonCation>
 
                 <thetaCation cation1="Na+" cation2="H+">
-                  <Theta> 0.036 </Theta>
+                  <theta> 0.036 </theta>
                 </thetaCation>
 
                 <psiCommonAnion anion="Cl-" cation1="Na+" cation2="H+">
-                  <Theta> 0.036 </Theta>
+                  <theta> 0.036 </theta>
                   <Psi> -0.004 </Psi>
                 </psiCommonAnion>
 
diff --git a/test_problems/cathermo/HMW_graph_CpvT/HMW_NaCl_sp1977_alt.xml b/test_problems/cathermo/HMW_graph_CpvT/HMW_NaCl_sp1977_alt.xml
index adaff9c71..abdbbb967 100644
--- a/test_problems/cathermo/HMW_graph_CpvT/HMW_NaCl_sp1977_alt.xml
+++ b/test_problems/cathermo/HMW_graph_CpvT/HMW_NaCl_sp1977_alt.xml
@@ -73,20 +73,20 @@
                 </binarySaltParameters>
 
                 <thetaAnion anion1="Cl-" anion2="OH-">
-                  <Theta> -0.05 </Theta>
+                  <theta> -0.05 </theta>
                 </thetaAnion>
 
                 <psiCommonCation cation="Na+" anion1="Cl-" anion2="OH-">
-                  <Theta> -0.05 </Theta>
+                  <theta> -0.05 </theta>
                   <Psi> -0.006 </Psi>
                 </psiCommonCation>
 
                 <thetaCation cation1="Na+" cation2="H+">
-                  <Theta> 0.036 </Theta>
+                  <theta> 0.036 </theta>
                 </thetaCation>
 
                 <psiCommonAnion anion="Cl-" cation1="Na+" cation2="H+">
-                  <Theta> 0.036 </Theta>
+                  <theta> 0.036 </theta>
                   <Psi> -0.004 </Psi>
                 </psiCommonAnion>
 
diff --git a/test_problems/cathermo/HMW_graph_GvI/HMW_NaCl.xml b/test_problems/cathermo/HMW_graph_GvI/HMW_NaCl.xml
index 93ff16c87..63a5fc6ce 100644
--- a/test_problems/cathermo/HMW_graph_GvI/HMW_NaCl.xml
+++ b/test_problems/cathermo/HMW_graph_GvI/HMW_NaCl.xml
@@ -66,20 +66,20 @@
                 </binarySaltParameters>
 
                 <thetaAnion anion1="Cl-" anion2="OH-">
-                  <Theta> -0.05 </Theta>
+                  <theta> -0.05 </theta>
                 </thetaAnion>
 
                 <psiCommonCation cation="Na+" anion1="Cl-" anion2="OH-">
-                  <Theta> -0.05 </Theta>
+                  <theta> -0.05 </theta>
                   <Psi> -0.006 </Psi>
                 </psiCommonCation>
 
                 <thetaCation cation1="Na+" cation2="H+">
-                  <Theta> 0.036 </Theta>
+                  <theta> 0.036 </theta>
                 </thetaCation>
 
                 <psiCommonAnion anion="Cl-" cation1="Na+" cation2="H+">
-                  <Theta> 0.036 </Theta>
+                  <theta> 0.036 </theta>
                   <Psi> -0.004 </Psi>
                 </psiCommonAnion>
 
diff --git a/test_problems/cathermo/HMW_graph_GvT/HMW_NaCl_sp1977_alt.xml b/test_problems/cathermo/HMW_graph_GvT/HMW_NaCl_sp1977_alt.xml
index adaff9c71..abdbbb967 100644
--- a/test_problems/cathermo/HMW_graph_GvT/HMW_NaCl_sp1977_alt.xml
+++ b/test_problems/cathermo/HMW_graph_GvT/HMW_NaCl_sp1977_alt.xml
@@ -73,20 +73,20 @@
                 </binarySaltParameters>
 
                 <thetaAnion anion1="Cl-" anion2="OH-">
-                  <Theta> -0.05 </Theta>
+                  <theta> -0.05 </theta>
                 </thetaAnion>
 
                 <psiCommonCation cation="Na+" anion1="Cl-" anion2="OH-">
-                  <Theta> -0.05 </Theta>
+                  <theta> -0.05 </theta>
                   <Psi> -0.006 </Psi>
                 </psiCommonCation>
 
                 <thetaCation cation1="Na+" cation2="H+">
-                  <Theta> 0.036 </Theta>
+                  <theta> 0.036 </theta>
                 </thetaCation>
 
                 <psiCommonAnion anion="Cl-" cation1="Na+" cation2="H+">
-                  <Theta> 0.036 </Theta>
+                  <theta> 0.036 </theta>
                   <Psi> -0.004 </Psi>
                 </psiCommonAnion>
 
diff --git a/test_problems/cathermo/HMW_graph_HvT/HMW_NaCl_sp1977_alt.xml b/test_problems/cathermo/HMW_graph_HvT/HMW_NaCl_sp1977_alt.xml
index adaff9c71..abdbbb967 100644
--- a/test_problems/cathermo/HMW_graph_HvT/HMW_NaCl_sp1977_alt.xml
+++ b/test_problems/cathermo/HMW_graph_HvT/HMW_NaCl_sp1977_alt.xml
@@ -73,20 +73,20 @@
                 </binarySaltParameters>
 
                 <thetaAnion anion1="Cl-" anion2="OH-">
-                  <Theta> -0.05 </Theta>
+                  <theta> -0.05 </theta>
                 </thetaAnion>
 
                 <psiCommonCation cation="Na+" anion1="Cl-" anion2="OH-">
-                  <Theta> -0.05 </Theta>
+                  <theta> -0.05 </theta>
                   <Psi> -0.006 </Psi>
                 </psiCommonCation>
 
                 <thetaCation cation1="Na+" cation2="H+">
-                  <Theta> 0.036 </Theta>
+                  <theta> 0.036 </theta>
                 </thetaCation>
 
                 <psiCommonAnion anion="Cl-" cation1="Na+" cation2="H+">
-                  <Theta> 0.036 </Theta>
+                  <theta> 0.036 </theta>
                   <Psi> -0.004 </Psi>
                 </psiCommonAnion>
 
diff --git a/test_problems/cathermo/HMW_graph_VvT/HMW_NaCl_sp1977_alt.xml b/test_problems/cathermo/HMW_graph_VvT/HMW_NaCl_sp1977_alt.xml
index adaff9c71..abdbbb967 100644
--- a/test_problems/cathermo/HMW_graph_VvT/HMW_NaCl_sp1977_alt.xml
+++ b/test_problems/cathermo/HMW_graph_VvT/HMW_NaCl_sp1977_alt.xml
@@ -73,20 +73,20 @@
                 </binarySaltParameters>
 
                 <thetaAnion anion1="Cl-" anion2="OH-">
-                  <Theta> -0.05 </Theta>
+                  <theta> -0.05 </theta>
                 </thetaAnion>
 
                 <psiCommonCation cation="Na+" anion1="Cl-" anion2="OH-">
-                  <Theta> -0.05 </Theta>
+                  <theta> -0.05 </theta>
                   <Psi> -0.006 </Psi>
                 </psiCommonCation>
 
                 <thetaCation cation1="Na+" cation2="H+">
-                  <Theta> 0.036 </Theta>
+                  <theta> 0.036 </theta>
                 </thetaCation>
 
                 <psiCommonAnion anion="Cl-" cation1="Na+" cation2="H+">
-                  <Theta> 0.036 </Theta>
+                  <theta> 0.036 </theta>
                   <Psi> -0.004 </Psi>
                 </psiCommonAnion>
 
diff --git a/test_problems/cathermo/HMW_test_1/HMW_NaCl.xml b/test_problems/cathermo/HMW_test_1/HMW_NaCl.xml
index 4b3cdea02..90682e9d3 100644
--- a/test_problems/cathermo/HMW_test_1/HMW_NaCl.xml
+++ b/test_problems/cathermo/HMW_test_1/HMW_NaCl.xml
@@ -56,16 +56,16 @@
                 </binarySaltParameters>
 
                 <thetaAnion anion1="Cl-" anion2="OH-">
-                  <Theta> -0.05 </Theta>
+                  <theta> -0.05 </theta>
                 </thetaAnion>
 
                 <psiCommonCation cation="Na+" anion1="Cl-" anion2="OH-">
-                  <Theta> -0.05 </Theta>
+                  <theta> -0.05 </theta>
                   <Psi> -0.006 </Psi>
                 </psiCommonCation>
 
                 <thetaCation cation1="Na+" cation2="H+">
-                  <Theta> 0.036 </Theta>
+                  <theta> 0.036 </theta>
                 </thetaCation>
 
                 <psiCommonAnion anion="Cl-" cation1="Na+" cation2="H+">
diff --git a/test_problems/cathermo/HMW_test_3/HMW_NaCl_tc.xml b/test_problems/cathermo/HMW_test_3/HMW_NaCl_tc.xml
index 2da3d2654..df910ae5f 100644
--- a/test_problems/cathermo/HMW_test_3/HMW_NaCl_tc.xml
+++ b/test_problems/cathermo/HMW_test_3/HMW_NaCl_tc.xml
@@ -64,20 +64,20 @@
                 </binarySaltParameters>
 
                 <thetaAnion anion1="Cl-" anion2="OH-">
-                  <Theta> -0.05 </Theta>
+                  <theta> -0.05 </theta>
                 </thetaAnion>
 
                 <psiCommonCation cation="Na+" anion1="Cl-" anion2="OH-">
-                  <Theta> -0.05 </Theta>
+                  <theta> -0.05 </theta>
                   <Psi> -0.006 </Psi>
                 </psiCommonCation>
 
                 <thetaCation cation1="Na+" cation2="H+">
-                  <Theta> 0.036 </Theta>
+                  <theta> 0.036 </theta>
                 </thetaCation>
 
                 <psiCommonAnion anion="Cl-" cation1="Na+" cation2="H+">
-                  <Theta> 0.036 </Theta>
+                  <theta> 0.036 </theta>
                   <Psi> -0.004 </Psi>
                 </psiCommonAnion>