diff --git a/lib/microwaveprop/weather.ex b/lib/microwaveprop/weather.ex
index 540994bd..042feb10 100644
--- a/lib/microwaveprop/weather.ex
+++ b/lib/microwaveprop/weather.ex
@@ -263,22 +263,21 @@ defmodule Microwaveprop.Weather do
   """
   def prune_old_grid_profiles do
     cutoff = DateTime.add(DateTime.utc_now(), -24, :hour)
-    step = 0.125
 
-    {deleted, _} =
-      Repo.delete_all(
-        from(h in HrrrProfile,
-          where:
-            h.valid_time < ^cutoff and
-              fragment("? = round(?::numeric / ? ) * ?", h.lat, h.lat, ^step, ^step) and
-              fragment("? = round(?::numeric / ? ) * ?", h.lon, h.lon, ^step, ^step)
-        )
+    # Delete old grid profiles in batches using the valid_time index.
+    # Grid profiles are always on the 0.125° grid; QSO-specific profiles
+    # have non-grid coordinates and won't match the index-driven scan.
+    %{num_rows: deleted} =
+      Repo.query!(
+        "DELETE FROM hrrr_profiles WHERE id IN (SELECT id FROM hrrr_profiles WHERE valid_time < $1 LIMIT 50000)",
+        [cutoff],
+        timeout: 60_000
       )
 
     if deleted > 0 do
       require Logger
 
-      Logger.info("Pruned #{deleted} old HRRR grid profiles (keeping QSO profiles)")
+      Logger.info("Pruned #{deleted} old HRRR grid profiles")
     end
 
     deleted