diff --git a/.drone.yml b/.drone.yml
index a529207..129bc4c 100644
--- a/.drone.yml
+++ b/.drone.yml
@@ -215,7 +215,7 @@ steps:
         echo "Postgres did not become available, aborting."
         exit 1
 
-  - name: test-slow
+  - name: test-all
     image: docker.io/library/elixir:1.18.3-otp-27
     environment:
       MIX_ENV: test
@@ -226,5 +226,5 @@ steps:
       - mix local.hex --force
       # Fetch dependencies
       - mix deps.get
-      # Run only all tests
+      # Run all tests (including slow/performance tests)
       - mix test
diff --git a/CODE_GUIDELINES.md b/CODE_GUIDELINES.md
index b11a369..3f43230 100644
--- a/CODE_GUIDELINES.md
+++ b/CODE_GUIDELINES.md
@@ -1656,7 +1656,7 @@ end
 
 **Performance Tests:**
 
-Performance tests that explicitly validate performance characteristics should be tagged with `@tag :slow` or `@moduletag :slow` to exclude them from standard test runs. This improves developer feedback loops while maintaining comprehensive coverage.
+Performance tests that explicitly validate performance characteristics should be tagged with `@tag :slow` or `@describetag :slow` to exclude them from standard test runs. This improves developer feedback loops while maintaining comprehensive coverage.
 
 **When to Tag as `:slow`:**
 
@@ -1664,6 +1664,12 @@ Performance tests that explicitly validate performance characteristics should be
 - Tests that use large datasets (e.g., 50+ records) to test scalability
 - Tests that validate query optimization (N+1 prevention, index usage)
 
+**Tagging Guidelines:**
+
+- Use `@tag :slow` for individual tests
+- Use `@describetag :slow` for entire describe blocks (not `@moduletag`, as it affects all tests in the module)
+- Performance tests should include measurable assertions (query counts, timing with tolerance, etc.)
+
 **Running Tests:**
 
 ```bash
@@ -1673,7 +1679,7 @@ mix test --exclude slow
 # Performance tests only
 mix test --only slow
 
-# All tests
+# All tests (including slow tests)
 mix test
 ```
 ---
diff --git a/docs/test-performance-optimization.md b/docs/test-performance-optimization.md
index cbff69f..6002f16 100644
--- a/docs/test-performance-optimization.md
+++ b/docs/test-performance-optimization.md
@@ -172,7 +172,7 @@ mix test
 #### CI/CD Integration
 
 - **Standard CI:** Runs `mix test --exclude slow` for faster feedback loops (~6 minutes)
-- **Nightly Builds:** Separate pipeline runs daily and executes `mix test --only slow` (~1.3 minutes)
+- **Nightly Builds:** Separate pipeline runs daily and executes `mix test` (all tests, including slow) for comprehensive coverage (~7.4 minutes)
 - **Pre-Merge:** Full test suite (`mix test`) runs before merging to main
 - **Manual Execution:** Can be triggered via Drone CLI or Web UI
 
@@ -535,13 +535,18 @@ mix test test/mv_web/member_live/index_member_fields_display_test.exs --slowest
 - Execution time: ~6 minutes
 - Command: `mix test --exclude slow` or `just test-fast`
 
-**Slow/Nightly Tests:**
-- Tests tagged with `@tag :slow` (25 tests)
+**Slow Tests:**
+- Tests tagged with `@tag :slow` or `@describetag :slow` (25 tests)
 - Low risk, >1 second execution time
-- UI/Display tests, workflow details, edge cases
+- UI/Display tests, workflow details, edge cases, performance tests
 - Execution time: ~1.3 minutes
 - Command: `mix test --only slow` or `just test-slow`
-- Run in nightly CI builds
+- Excluded from standard CI runs
+
+**Nightly CI Builds:**
+- Runs all tests (`mix test`) for comprehensive coverage
+- Execution time: ~7.4 minutes
+- Ensures full test coverage including slow/performance tests
 
 **All Tests:**
 - Includes both fast and slow tests
@@ -692,13 +697,13 @@ A: Monitor for 2-3 months. If no seeds-related bugs appear that would have been
 A: Consider running the full test suite (including slow tests) before major releases. Daily development uses the optimized suite.
 
 **Q: How do I add a new performance test?**  
-A: Tag it with `@tag :slow` or `@moduletag :slow`. See "Performance Test Guidelines" section above.
+A: Tag it with `@tag :slow` for individual tests or `@describetag :slow` for describe blocks. Use `@describetag` instead of `@moduletag` to avoid tagging unrelated tests. Include measurable performance assertions (query counts, timing with tolerance, etc.). See "Performance Test Guidelines" section above.
 
 **Q: Can I run slow tests locally?**  
 A: Yes, use `just test-slow` or `mix test --only slow`. They're excluded from standard runs for faster feedback.
 
 **Q: What is the "nightly suite"?**  
-A: The "nightly suite" refers to tests tagged with `@tag :slow`. We use a single tag (`:slow`) for both performance tests and tests suitable for nightly execution. All tests tagged with `:slow` are excluded from standard runs and can be executed in nightly CI builds. 
+A: The "nightly suite" refers to the nightly CI pipeline that runs **all tests** (`mix test`), including slow tests. Tests tagged with `@tag :slow` or `@describetag :slow` are excluded from standard CI runs for faster feedback, but are included in the nightly full test suite for comprehensive coverage. 
 
 **Q: Which tests should I tag as `:slow`?**  
 A: Tag tests with `@tag :slow` if they: (1) take >1 second, (2) have low risk (not critical for catching regressions), and (3) test UI/Display/Formatting or workflow details. See "Test Tagging Guidelines" section for details.
diff --git a/test/mv_web/live/group_live/index_test.exs b/test/mv_web/live/group_live/index_test.exs
index e844bcc..8ce3e58 100644
--- a/test/mv_web/live/group_live/index_test.exs
+++ b/test/mv_web/live/group_live/index_test.exs
@@ -114,17 +114,36 @@ defmodule MvWeb.GroupLive.IndexTest do
     end
   end
 
-  @moduletag :slow
   describe "performance" do
+    @describetag :slow
     test "page loads efficiently with many groups", %{conn: conn} do
       # Create multiple groups
       Enum.each(1..10, fn _ -> Fixtures.group_fixture() end)
 
+      # Count queries using Telemetry
+      query_count_agent = Agent.start_link(fn -> 0 end) |> elem(1)
+
+      handler = fn _event, _measurements, _metadata, _config ->
+        Agent.update(query_count_agent, &(&1 + 1))
+      end
+
+      handler_id = "test-query-counter-#{System.unique_integer([:positive])}"
+      :telemetry.attach(handler_id, [:ash, :query, :start], handler, nil)
+
       # Should load without N+1 queries
       {:ok, _view, html} = live(conn, "/groups")
 
+      final_count = Agent.get(query_count_agent, & &1)
+      :telemetry.detach(handler_id)
+
       # Verify all groups are displayed
       assert html =~ gettext("Groups")
+
+      # Verify query count is reasonable (should avoid N+1 queries)
+      # Expected: 1 query for groups list + possible count queries
+      # Allow some overhead for LiveView setup queries
+      assert final_count <= 5,
+             "Expected max 5 queries (groups list + possible counts + LiveView setup), got #{final_count}. This suggests N+1 query problem."
     end
 
     test "member count is loaded efficiently via calculation", %{conn: conn} do
@@ -143,10 +162,29 @@ defmodule MvWeb.GroupLive.IndexTest do
         actor: system_actor
       )
 
+      # Count queries using Telemetry
+      query_count_agent = Agent.start_link(fn -> 0 end) |> elem(1)
+
+      handler = fn _event, _measurements, _metadata, _config ->
+        Agent.update(query_count_agent, &(&1 + 1))
+      end
+
+      handler_id = "test-query-counter-#{System.unique_integer([:positive])}"
+      :telemetry.attach(handler_id, [:ash, :query, :start], handler, nil)
+
       {:ok, _view, html} = live(conn, "/groups")
 
+      final_count = Agent.get(query_count_agent, & &1)
+      :telemetry.detach(handler_id)
+
       # Member count should be displayed (should be 2)
       assert html =~ "2" or html =~ gettext("Members") or html =~ "Mitglieder"
+
+      # Verify query count is reasonable (member count should be calculated efficiently)
+      # Expected: 1 query for groups + 1 query for member counts (aggregated)
+      # Allow some overhead for LiveView setup queries
+      assert final_count <= 5,
+             "Expected max 5 queries (groups + member counts + LiveView setup), got #{final_count}. This suggests inefficient member count calculation."
     end
   end
 end
diff --git a/test/mv_web/live/group_live/show_test.exs b/test/mv_web/live/group_live/show_test.exs
index 177318e..50424ac 100644
--- a/test/mv_web/live/group_live/show_test.exs
+++ b/test/mv_web/live/group_live/show_test.exs
@@ -219,8 +219,8 @@ defmodule MvWeb.GroupLive.ShowTest do
     end
   end
 
-  @moduletag :slow
   describe "performance" do
+    @describetag :slow
     test "member list is loaded efficiently (no N+1 queries)", %{conn: conn} do
       group = Fixtures.group_fixture()
 
@@ -236,12 +236,31 @@ defmodule MvWeb.GroupLive.ShowTest do
         )
       end)
 
+      # Count queries using Telemetry
+      query_count_agent = Agent.start_link(fn -> 0 end) |> elem(1)
+
+      handler = fn _event, _measurements, _metadata, _config ->
+        Agent.update(query_count_agent, &(&1 + 1))
+      end
+
+      handler_id = "test-query-counter-#{System.unique_integer([:positive])}"
+      :telemetry.attach(handler_id, [:ash, :query, :start], handler, nil)
+
       {:ok, _view, html} = live(conn, "/groups/#{group.slug}")
 
+      final_count = Agent.get(query_count_agent, & &1)
+      :telemetry.detach(handler_id)
+
       # All members should be displayed
       Enum.each(members, fn member ->
         assert html =~ member.first_name or html =~ member.last_name
       end)
+
+      # Verify query count is reasonable (should avoid N+1 queries)
+      # Expected: 1 query for group lookup + 1 query for members (with preload)
+      # Allow some overhead for LiveView setup queries
+      assert final_count <= 5,
+             "Expected max 5 queries (group + members preload + LiveView setup), got #{final_count}. This suggests N+1 query problem."
     end
 
     test "slug lookup is efficient (uses unique_slug index)", %{conn: conn} do