Bearing in mind that you were asking for advice on 23 April and seemed to have added fish by 3 May, i dont think you have cycled your tank properly. Although things will look OK to begin with, if you're not careful things will rapidly go wrong. Read up about in the cycling section. As you already have fish, then you are into a 'fish-in cycle' which is not good news for the fish. You must check your water every day and be prepared to do very frequent water changes to keep thing stable until the filter has cycled. What sort of filter does your tank have?