I know I build things for fish to live in, but why is it called an aquarium?
I  have a big Aquarium in my back yard , is a vivarium of any size having at least one transparent side in which aquatic plants or animals are kept
oh cool!  What kind of fish can go in them?
As a Fishkeepers use aquaria to keep fish, invertebrates, amphibians, aquatic reptiles such as turtles
Can I just put water in there?  Or is there anything else I need to do?
Well,its simply .is a water-filled tank in which fish swim about
How long have people had aquariums for?
The Aquarium: An Unveiling of the Wonders of the Deep Sea" in 1854.
Ok I'll have to check that out thanks!
For the records, aquarium principle was fully developed in 1850 by the chemist Robert Warington, who explained that plants added to water in a container would give off enough oxygen to support animals, so long as the numbers of animals did not grow too large.