Looks silly doesnt it? but this is the basic sysstem when you are trying to device an aquatic community. Tank" + "Fish = you get a natural biotope right inside your home. Depending on how you will set up the tank, then its up to you. In My personal experience I like Freshwater biotope more than the saltwater. The basic here is putting something alive into your tank, it doesnt necessarily mean that if you put an aerator it necessarily means that it is already a nice environment for the organisms in the tank like fishes and plants. Other experts in aqua culture use no aeration or CO2 what so ever to support life in the tank. All they have is a very very patient behaviour waiting for months, after setting up plants and fishes, before they could live their aquarium life sustaining on its own. So Tank" + "Fish? Its up to you to decide.