diff --git a/api/s20_mixing.py b/api/s20_mixing.py
index 1a43465..1b8917c 100644
--- a/api/s20_mixing.py
+++ b/api/s20_mixing.py
@@ -13,7 +13,9 @@ def get_mixing_schema(name: str) -> dict[str, dict[str, Any]]:
 
 
 def get_mixing(name: str, tank: str) -> dict[str, Any]:
-    m = read(name, f"select * from mixing where tank = '{tank}'")
+    m = try_read(name, f"select * from mixing where tank = '{tank}'")
+    if m == None:
+        return {}
     d = {}
     d['tank'] = str(m['tank'])
     d['model'] = str(m['model'])
@@ -61,6 +63,10 @@ def set_mixing_cmd(name: str, cs: ChangeSet) -> DbChangeSet:
 
 
 def set_mixing(name: str, cs: ChangeSet) -> ChangeSet:
+    if 'tank' not in cs.operations[0]:
+        return ChangeSet()
+    if get_mixing(name, cs.operations[0]['tank']) == {}:
+        return ChangeSet()
     return execute_command(name, set_mixing_cmd(name, cs))
 
 
@@ -77,6 +83,10 @@ def add_mixing_cmd(name: str, cs: ChangeSet) -> DbChangeSet:
 
 
 def add_mixing(name: str, cs: ChangeSet) -> ChangeSet:
+    if 'tank' not in cs.operations[0]:
+        return ChangeSet()
+    if get_mixing(name, cs.operations[0]['tank']) != {}:
+        return ChangeSet()
     return execute_command(name, add_mixing_cmd(name, cs))
 
 
@@ -93,6 +103,10 @@ def delete_mixing_cmd(name: str, cs: ChangeSet) -> DbChangeSet:
 
 
 def delete_mixing(name: str, cs: ChangeSet) -> ChangeSet:
+    if 'tank' not in cs.operations[0]:
+        return ChangeSet()
+    if get_mixing(name, cs.operations[0]['tank']) == {}:
+        return ChangeSet()
     return execute_command(name, delete_mixing_cmd(name, cs))
 
 
diff --git a/test_tjnetwork.py b/test_tjnetwork.py
index c95e66c..ba39f98 100644
--- a/test_tjnetwork.py
+++ b/test_tjnetwork.py
@@ -3036,6 +3036,8 @@ class TestApi:
 
         add_tank(p, ChangeSet({'id': 't0', 'x': 0.0, 'y': 10.0, 'elevation': 20.0, 'init_level': 1.0, 'min_level': 0.0, 'max_level': 2.0, 'diameter': 10.0, 'min_vol': 100.0, 'vol_curve': None, 'overflow': OVERFLOW_NO}))
 
+        assert get_mixing(p, 't0') == {}
+
         add_mixing(p, ChangeSet({'tank': 't0', 'model': MIXING_MODEL_MIXED, 'value': 10.0}))
         m = get_mixing(p,'t0')
         assert m['tank'] == 't0'
@@ -3056,6 +3058,8 @@ class TestApi:
 
         delete_mixing(p, ChangeSet({'tank': 't0'}))
 
+        assert get_mixing(p, 't0') == {}
+
         self.leave(p)