diff --git a/changelog.txt b/changelog.txt
index dee2f7d..7636c26 100644
--- a/changelog.txt
+++ b/changelog.txt
@@ -1,13 +1,15 @@
 ---------------------------------------------------------------------------------------------------
 Version: 0.18.3
 Date: 2020-03-21
+  Changes:
+    - Migrated on_event to on_nth_tick for performance
   Bugfixes:
     - Added missing initialization of turret index
 ---------------------------------------------------------------------------------------------------
 Version: 0.18.2
 Date: 2020-03-20
   Changes:
-    - Redesigned surface handling again to be more perfomant
+    - Redesigned surface handling again to be more performant
 ---------------------------------------------------------------------------------------------------
 Version: 0.18.1
 Date: 2020-03-19
diff --git a/control.lua b/control.lua
index 46b025a..d8c2a32 100644
--- a/control.lua
+++ b/control.lua
@@ -1,33 +1,36 @@
 --control.lua
 --This mod scans the map for gun-turrets and places alerts when turrets are low. 
 
-script.on_event({defines.events.on_tick}, function (event)
-	--Every minute the surface is rescanned for ammo-turret type entities. This is stored in the global table. 
-	if event.tick%3600 == 0 or global.turret_entities == nil then
-		global.turret_entities = {}
-		for index,surface in pairs(game.surfaces) do
-			global.turret_entities[index] = surface.find_entities_filtered{type = "ammo-turret"}
-		end
-	end
-	if event.tick%600 == 0 then
-	--Every 10 seconds recheck and give alerts to players for ammo-turret entities on the same force as them. 
-		for _,player in pairs(game.connected_players) do
-			
-			GTA_enabled = player.mod_settings["gun-turret-alerts-enabled"].value
-			player_threshold = player.mod_settings["gun-turret-alerts-threshold"].value
-			turret_entities = global.turret_entities[player.surface.name]
+script.on_init(function (event)
+	-- turret index init
+	global.turret_entities = {}
+end)
 
-			if GTA_enabled and turret_entities then
-				for _,turret_entity in pairs(turret_entities) do
-					if turret_entity.valid and turret_entity.force == player.force then
-						inv_var = turret_entity.get_inventory(defines.inventory.turret_ammo)
-						if inv_var.is_empty() then
-							-- no ammo alert
-							player.add_custom_alert(turret_entity, {type = "item", name = "piercing-rounds-magazine"}, "Out of ammo", true)
-						elseif inv_var[1].count < player_threshold then
-							-- low ammo alert
-							player.add_custom_alert(turret_entity, {type = "item", name = "firearm-magazine"}, "Ammo low", true)
-						end
+script.on_nth_tick(3600, function (event)
+	--Every minute the surface is rescanned for ammo-turret type entities. This is stored in the global table. 
+	for index,surface in pairs(game.surfaces) do
+		global.turret_entities[index] = surface.find_entities_filtered{type = "ammo-turret"}
+	end
+end)
+
+script.on_nth_tick(600, function (event)
+	--Every 10 seconds recheck and give alerts to players for ammo-turret entities on the same force as them. 
+	for _,player in pairs(game.connected_players) do
+		
+		GTA_enabled = player.mod_settings["gun-turret-alerts-enabled"].value
+		player_threshold = player.mod_settings["gun-turret-alerts-threshold"].value
+		turret_entities = global.turret_entities[player.surface.name]
+
+		if GTA_enabled and turret_entities then
+			for _,turret_entity in pairs(turret_entities) do
+				if turret_entity.valid and turret_entity.force == player.force then
+					inv_var = turret_entity.get_inventory(defines.inventory.turret_ammo)
+					if inv_var.is_empty() then
+						-- no ammo alert
+						player.add_custom_alert(turret_entity, {type = "item", name = "piercing-rounds-magazine"}, "Out of ammo", true)
+					elseif inv_var[1].count < player_threshold then
+						-- low ammo alert
+						player.add_custom_alert(turret_entity, {type = "item", name = "firearm-magazine"}, "Ammo low", true)
 					end
 				end
 			end