First Saltwater Aquarium

Hi Classicxsarah,

I have had my fair share of reef tanks so I am pretty knowledgable about it. To me, the biggest difference between a saltwater tank and a freshwater tank is the filtration. With a freshwater fish tank you use a hang on back filter or some other form of mechanical filtration. With a saltwater tank you use live rock and live sand as a biological filter. This is probably the biggest change in thinking that is required when switching from fresh to saltwater.

The other obvious difference is the salt in the water. I have used most of the commercially available salt mixes and all of them are adequate unless you start getting into high end SPS corals (small polyp stoney corals). There are really two ways for the home aquarist to measure salt in a marine tank. The first is with a hydrometer and the second is with a refractometer. A refractometer is far more accurate but also more expensive. For the beginner, a hydrometer should be fine. Under no circumstances should you mix water per the directions and call it good. It needs to be measured with a hydrometer or refractometer. Also, as water evaporates from a saltwater tank, the salt level rises so you have to keep adding fresh water to the tank (usually daily) to keep the salinity levels in line.

So now that I've rambled on a bit - here is the list you asked for:

NEEDS:
Fish tank/Stand
Heater
Live Rock (You can actually use dead rock such as reef bones and the like but you will need at least a few pounds of real live rock to "seed" the system)
Aragonite Sand (Just buy plain old dry aragonite sand. The sand that comes as "live sand" sealed in a bag is just a waste of money)
Salt mix (Instant Ocean, Red Sea, etc)
Hydrometer or refractometer
Dechlorinator if you plan on using tap water

MIGHT NEED TO HAVE:
RO/DI System (If your tap water has too many bad trace elements)
Protein Skimmer (You can get by without one but it will reduce the amount of water changes needed. Also, this is really more of a need if you plan on keeping corals)
A Clean up crew (Snails, hermit crabs, etc. These are needed for a reef tank that is going to have corals in it. If it is going to be a fish only system you don't need these but can still have them if your fish won't eat them.)
Adequate lighting (If you are going to keep corals I recommend T5 High Output lighting. Don't scrimp here if you can help it. PC lighting just can't compete.)

NICE TO HAVE:
Refractometer
A sump with overflow/return pump

That pretty much covers the basics I think. If you let me know what type of tank you want (reef tank, fowler tank, SPS tank, etc I can give you better advice)