diff --git a/enviro/__init__.py b/enviro/__init__.py
index 17fa3a4..f088ea5 100644
--- a/enviro/__init__.py
+++ b/enviro/__init__.py
@@ -421,7 +421,7 @@ def get_sensor_readings():
 def save_reading(readings):
   # open todays reading file and save readings
   helpers.mkdir_safe("readings")
-  readings_filename = f"readings/{helpers.datetime_file_string()}.txt"
+  readings_filename = f"readings/{helpers.date_string()}.txt"
   new_file = not helpers.file_exists(readings_filename)
   with open(readings_filename, "a") as f:
     if new_file: