diff --git a/core/transformations.py b/core/transformations.py
index 955d5a4..bda22c1 100644
--- a/core/transformations.py
+++ b/core/transformations.py
@@ -299,11 +299,15 @@ def _build_substring_removal_clauses(client: bigquery.Client, source_table: str,
     
     # Identify columns that need substring removal
     subset_columns = []
-    for col in all_columns:
+    for col in subset_columns:
         # Skip already processed columns
         if col.lower() in processed_columns:
             continue
-            
+
+        # Skip loop variables so they get processed in the loop variable step
+        if utils.extract_loop_number(col) is not None:
+            continue
+
         # Check if any substring from constants.SUBSTRINGS_TO_FIX is in the column name
         if any(substring in col for substring in constants.SUBSTRINGS_TO_FIX):
             subset_columns.append(col)