diff --git a/app/assets/javascripts/editor.js b/app/assets/javascripts/editor.js
index cf57c08f..f67d1fb5 100644
--- a/app/assets/javascripts/editor.js
+++ b/app/assets/javascripts/editor.js
@@ -1127,6 +1127,10 @@ $(function() {
 
   var initTurtle = function() {
       // todo guard clause if turtle is not required for the current exercise
+
+      // clear canvas
+      // turtlecanvas.getContext("2d").clearRect(0, 0, turtlecanvas.width, turtlecanvas.height);
+
       turtlescreen = new Turtle(websocket, turtlecanvas);
       if ($('#run').isPresent()) {
         $('#run').bind('click', hideCanvas);
diff --git a/lib/docker_client.rb b/lib/docker_client.rb
index 0c34f6e3..4a353394 100644
--- a/lib/docker_client.rb
+++ b/lib/docker_client.rb
@@ -218,7 +218,7 @@ class DockerClient
     """
     Run commands by attaching a websocket to Docker.
     """
-    command = submission.execution_environment.send(:"run_command") % command_substitutions(filename)
+    command = submission.execution_environment.run_command % command_substitutions(filename)
     create_workspace_files = proc { create_workspace_files(container, submission) }
     execute_websocket_command(command, create_workspace_files, block)
   end
@@ -227,7 +227,7 @@ class DockerClient
     """
     Stick to existing Docker API with exec command.
     """
-    command = submission.execution_environment.send(:"test_command") % command_substitutions(filename)
+    command = submission.execution_environment.test_command % command_substitutions(filename)
     create_workspace_files = proc { create_workspace_files(container, submission) }
     execute_command(command, create_workspace_files, block)
   end
diff --git a/lib/docker_container_pool.rb b/lib/docker_container_pool.rb
index 320b9a1d..d027076b 100644
--- a/lib/docker_container_pool.rb
+++ b/lib/docker_container_pool.rb
@@ -83,10 +83,13 @@ class DockerContainerPool
   def self.refill_for_execution_environment(execution_environment)
     refill_count = [execution_environment.pool_size - @all_containers[execution_environment.id].length, config[:refill][:batch_size]].min
     if refill_count > 0
-      Rails.logger.info('adding ' + refill_count.to_s + ' containers for  ' +  execution_environment.name )
+      Rails.logger.info('Adding ' + refill_count.to_s + ' containers for execution_environment ' +  execution_environment.name )
       c = refill_count.times.map { create_container(execution_environment) }
+      Rails.logger.debug('Created containers: ' + c.to_s )
       @containers[execution_environment.id] += c
       @all_containers[execution_environment.id] += c
+      Rails.logger.debug('@containers ' + @containers.object_id.to_s + ' has:'+ @containers[execution_environment.id].to_s)
+      Rails.logger.debug('@all_containers '  + @containers.object_id.to_s + ' has:'+ @all_containers[execution_environment.id].to_s)
       #refill_count.times.map { create_container(execution_environment) }
     end