People regularly ask why we don't have any saltwater tanks. For as complicated as we make our freshwater tanks, saltwater is many times beyond that. If it were merely that, I would be up for the challenge, but it comes at tremendous cost as well. One mistake and you might kill everything in your tank. While such mistakes can be made in freshwater, it is generally more forgiving and even if it does happen, your losses are a fraction of what they would be in a marine tank. Saltwater fish generally start at the high end of what we pay for freshwater fish, and corals average twice that and up up steeply from there. Different fish and corals require different minerals and chemical parameters to be dosed/monitored. As with anything, you can make it as complicated as you want, and allot depends on the specific fish and corals you wish to keep, but the photos below are an example of what it takes to do it right:
Here is another one, it's clearly a high-end tank, but it has great pictures of its equipment room.
Saltwater is cool, and someday I will probably have a marine tank, but not until I can afford to do it right, and possibly hire someone to do the maintenance.