I blog about salt water aquarium as everyone seems to love a  marine aquarium that  keeps marine plants and animals in a contained environment.
Interesting. What are the best fish to keep in a salt water aquarium?
I will just talk in general about an aquarium. You can find fish, invertebrates, amphibians, aquatic reptiles such as turtles, and aquatic plants in an aquarium
Cool. What type of people seem to most enjoy aquariums? 
Most times they are hobbyist and the categorized the aquarium to be  fish only (FO), fish only with live rock (FOWLR), and reef aquaria.
I see. Is it expensive to maintain an aquarium? 
Yes, to get what will live in there. The inhabitants  are often difficult to acquire and are usually more expensive than freshwater aquarium inhabitants.