diff --git a/netforce_clinic/models/hd_case.py b/netforce_clinic/models/hd_case.py
index 817c1db..450195b 100644
--- a/netforce_clinic/models/hd_case.py
+++ b/netforce_clinic/models/hd_case.py
@@ -607,7 +607,7 @@ class HDCase(Model):
                 dlz=dlz_line.dialyzer_id
                 use_time=dlz_line.use_time or 0
                 if is_decrease:
-                    use_time-=use_time
+                    use_time-=1
                     print("decrease ok")
                 print("use_time ", use_time)
                 if dlz_line.use_time < dlz.max_use_time: