diff --git a/pcpostprocess/hergQC.py b/pcpostprocess/hergQC.py
index 9356173..ceb04e3 100644
--- a/pcpostprocess/hergQC.py
+++ b/pcpostprocess/hergQC.py
@@ -410,8 +410,6 @@ def qc5(self, recording1, recording2, win=None, label=''):
         max_diff = recording1[i:f][wherepeak] - recording2[i:f][wherepeak]
         max_diffc = self.max_diffc * recording1[i:f][wherepeak]
 
-        logging.debug(f"qc5: max_diff = {max_diff}, max_diffc = {max_diffc}")
-
         if (max_diff < max_diffc) or not (np.isfinite(max_diff)
                                           and np.isfinite(max_diffc)):
             self.logger.debug(f"max_diff:  {max_diff}, max_diffc: {max_diffc}")
diff --git a/tests/test_herg_qc.py b/tests/test_herg_qc.py
index 5b47896..af924ec 100644
--- a/tests/test_herg_qc.py
+++ b/tests/test_herg_qc.py
@@ -146,7 +146,7 @@ def test_qc3(self):
             recording0 = np.asarray([0, 1] * 1000)
             recording1 = recording0 + i
             result = hergqc.qc3(recording0, recording1)
-            self.assertEqual(result[0], expected, f"({result[1]})")
+            self.assertEqual(result[0], expected, f"({i}: {result[1]})")
 
         # TODO: Test on select data
 
@@ -206,7 +206,41 @@ def test_qc5(self):
             recording0 = np.asarray([0, 1] * 1000)
             recording1 = recording0 + i
             result = hergqc.qc5(recording0, recording1)
-            self.assertEqual(result[0], expected, f"({result[1]})")
+            self.assertEqual(result[0], expected, f"({i}: {result[1]})")
+
+        # TODO: Test on select data
+
+    def test_qc5_1(self):
+        plot_dir = os.path.join(self.output_dir, "test_qc5")
+        if not os.path.exists(plot_dir):
+            os.makedirs(plot_dir)
+
+        hergqc = hERGQC(
+            sampling_rate=self.sampling_rate, plot_dir=plot_dir, voltage=self.voltage
+        )
+
+        # qc5_1 checks that the RMSD to zero of staircase protocol changes 
+        # by at least 50% of the raw trace after E-4031 addition.
+        test_matrix = [
+            (0.1, True),
+            (0.2, True),
+            (0.3, True),
+            (0.4, True),
+            (0.49, True),
+            (0.5, True),
+            (0.51, False),
+            (0.6, False),
+            (0.7, False),
+            (0.8, False),
+            (0.9, False),
+            (1.0, False),
+        ]
+
+        for i, expected in test_matrix:
+            recording0 = np.asarray([0, 1] * 1000)
+            recording1 = recording0 * i
+            result = hergqc.qc5_1(recording0, recording1)
+            self.assertEqual(result[0], expected, f"({i}: {result[1]})")
 
         # TODO: Test on select data