diff --git a/interfaces/dotnet/Cantera.Tests/src/EnumsTest.cs b/interfaces/dotnet/Cantera.Tests/src/EnumsTest.cs
index a2be7a4c8c4..04995dcc9c9 100644
--- a/interfaces/dotnet/Cantera.Tests/src/EnumsTest.cs
+++ b/interfaces/dotnet/Cantera.Tests/src/EnumsTest.cs
@@ -37,10 +37,6 @@ public void ThermoPair_ToStringsCorrectly()
         }
     }
 
-    [Fact]
-    public void EquilibriumSolver_MapsCorrectly() =>
-        TestInteropEnumInvariants<EquilibriumSolver>(true, -1, 2);
-
     [Fact]
     public void LogLevel_MapsCorrectly() =>
         TestInteropEnumInvariants<LogLevel>(true, 0, 2);
diff --git a/interfaces/dotnet/Cantera/src/DataDirectoryCollection.cs b/interfaces/dotnet/Cantera/src/DataDirectoryCollection.cs
index 1d89c71971e..c831586e62f 100644
--- a/interfaces/dotnet/Cantera/src/DataDirectoryCollection.cs
+++ b/interfaces/dotnet/Cantera/src/DataDirectoryCollection.cs
@@ -46,7 +46,7 @@ public void Add(string dir) =>
     public void Add(DirectoryInfo dir)
     {
         InteropUtil.CheckReturn(LibCantera.ct_addCanteraDirectory(
-            (nuint) dir.FullName.Length, dir.FullName));
+            dir.FullName.Length, dir.FullName));
 
         _dirs.Clear();
         _dirs.AddRange(GetDirs());
diff --git a/interfaces/dotnet/Cantera/src/Enums.cs b/interfaces/dotnet/Cantera/src/Enums.cs
index 4399d107bf0..a171edbef8e 100644
--- a/interfaces/dotnet/Cantera/src/Enums.cs
+++ b/interfaces/dotnet/Cantera/src/Enums.cs
@@ -103,32 +103,6 @@ public static string ToInteropString(this ThermoPair thermoPair)
 
 // the constants MUST match what CLIB is expecting
 
-/// <summary>
-/// Determines which algorithm is used to find equilibrium.
-/// </summary>
-public enum EquilibriumSolver
-{
-    /// <summary>
-    /// Allow Cantera to determine the optimum algorithm.
-    /// </summary>
-    Auto = -1,
-
-    /// <summary>
-    /// Solve by using the element potential algorithm.
-    /// </summary>
-    ElementPotential,
-
-    /// <summary>
-    /// Solve by using the general algorithm to minimize Gibbs free energy.
-    /// </summary>
-    Gibbs,
-
-    /// <summary>
-    /// Solved by using the VCS algorithm to minimize Gibbs free energy.
-    /// </summary>
-    Vcs
-}
-
 /// <summary>
 /// The
 /// </summary>
diff --git a/interfaces/dotnet/Cantera/src/SpeciesCollection.cs b/interfaces/dotnet/Cantera/src/SpeciesCollection.cs
index 348a1ecc5dd..3e6138f03d1 100644
--- a/interfaces/dotnet/Cantera/src/SpeciesCollection.cs
+++ b/interfaces/dotnet/Cantera/src/SpeciesCollection.cs
@@ -12,6 +12,8 @@ namespace Cantera;
 /// </summary>
 public class SpeciesCollection : IReadOnlyList<Species>
 {
+    readonly SolutionHandle _sol;
+
     readonly ThermoPhaseHandle _handle;
 
     // this collection should be eagerly-initialized because it depends on interop
diff --git a/interfaces/dotnet/Cantera/src/ThermoPhase.cs b/interfaces/dotnet/Cantera/src/ThermoPhase.cs
index fb9f5ddab7a..8a3e3815eb8 100644
--- a/interfaces/dotnet/Cantera/src/ThermoPhase.cs
+++ b/interfaces/dotnet/Cantera/src/ThermoPhase.cs
@@ -51,9 +51,11 @@ static ThermoPhase()
     /// </summary>
     public SpeciesCollection Species => _species.Value;
 
-    internal ThermoPhase(string filename, string? phaseName)
+    internal ThermoPhase(string filename, string? phaseName, string? transModel)
     {
-        _handle = LibCantera.thermo_newFromFile(filename, phaseName ?? "");
+        _sol = LibCantera.soln_newSolution(
+            filename, phaseName ?? "", transModel ?? "default");
+        _handle = LibCantera.soln_thermo(_sol);
         _handle.EnsureValid();
 
         _species = new(() => new SpeciesCollection(_handle));
@@ -61,17 +63,16 @@ internal ThermoPhase(string filename, string? phaseName)
 
     /// <summary>
     /// Simulates bringing the phase to thermodynamic equilibrium by holding the
-    /// specified <see cref="ThermoPair" /> constant and using the algorithm
-    /// identified by the given <see cref="EquilibriumSolver" />.
+    /// specified <see cref="ThermoPair" /> constant and using the identified algorithm.
     /// </summary>
     public void Equilibrate(ThermoPair thermoPair,
-                            EquilibriumSolver solver = EquilibriumSolver.Auto,
+                            string algorithm = "auto",
                             double tolerance = 1e-9, int maxSteps = 1000,
                             int maxIterations = 100, int logVerbosity = 0)
     {
         var interopString = thermoPair.ToInteropString();
 
-        var retVal = LibCantera.thermo_equilibrate(_handle, interopString, (int) solver,
+        var retVal = LibCantera.thermo_equilibrate(_handle, interopString, algorithm,
             tolerance, maxSteps, maxIterations, logVerbosity);
 
         InteropUtil.CheckReturn(retVal);