Hi I set up my first marine tank on the 15/5/16 a marine Kent 94l have 16kg of live rock on display and another 2kg in the back sump with filter floss carbon and phosphate remover all levels look good and have been coming down gradually apart from ammonia which has been 0.15 for the last 5 days is this normal and will go down when its ready to or should I do a water change on the tank not sure what to do for the best thanks