Gravel is good because it harbors beneficial bacteria. Acclimating the fish by floating the bag only acclimates the fish to the temperature, not the water.
Im sorry to rain on your setup, because i am a clean water freak, but: proper aquariums need to have water changed 25% each month if not every other week. Goldfish especially are very dirty fish. Even with a filter it won't be picking up all you think it is. I know that when I start to vacuum my...