i recently set up a new aquarium, its a juwell korall 60 , 54l. let it run for a week without fish, added 2 cherry barbs and 2 gold barbs 3 days ago and have been testing water for ammonia using nutrifin testing kit, the test keep coming up yellow , on the chart this is good ( no ammonia ) ph is 6.8, when should i start seeing ammonia levels rise ?