To the above there is no such thing as instant cycling, the nitrogen cycle does not sublimely manifest itself in tanks just by adding a biological agent, it takes time to break in, under all circumstances, that why you always have an nitrate spike when you add your fish into your tank.
I recommend the following if you want to jump into saltwater
first off is the tank, 55 gallon standard is probably the safest route to go, make sure you rinse out the tank when you get it
Second filitration, this is where many people go wrong because it all depends on what kind of saltwater tank you will be attempting, if it is just a fish only, I recomend first a skimmer (it gets rid of the execess proteins by use of very fine bubbles and is essential for all saltwater tanks unless you want to do biweekly water changes it also helps to oxygenate the tank) and a very heavy duty canister or wet dry filter; Some fish only aquariums wont need as much filtration i.e. canister filter, but I still recommend it for a beginner because they can be more efficient . If you are planning on add-in corals, do not go with wet dry or a canister filter because the extra waste that builds up in them will cause nitrates to build up quickly and although your fish may handle those at certain levels, corals will not (excluding a few soft corals) Instead I recommend a skimmer and a scump with filtration components, and several heavy duty power heads to help break down organic material so the skimmer will work more effectively. I also recommend that you do not use an air driven skimmer for reef tanks above 30 gallons, instead use an Impeller driven one with an air tube attached somewhere, they are far more effective.
Next is lighting, if you are going with a fish only, then you wonít need heavy-duty lighting. But if you get a reef tank you may need to invest in some serious equipment, I suggest power compact fluorescentís, with a Kelvin rating (color temperature) above 10,000 for enact bulb, for a 55 gallon you may want 4x55 watt bulbs, that should maintain easier to keep corals like soft corals, which are also the easier to keep. If you want to keep hard corals I recommend a metal halide system, but I don't recommend you keeping hard corals if you are a beginner, try soft for a few years then graduate to hard later.
First live rock- this stuff is ALIVE, you have to buy it at a pet store which specializes in saltwater fish, the rock contains coralline algae and nitrate nitrifying bacteria which is a major component in the filtration of saltwater fish tanks. Also this is central to the cycling process of saltwater tanks.
For fish, I also recommend damsel for beginners, they are beautiful, yet extremely hardy littlie buggers, and are basically the karp of the sea and are probably the cheapest fish in the saltwater section (averaging about 3.50 a fish), they can handle incredibly horrible water conditions and are perfect for cycling. I have never had one die on me in cycling process even when I accidentally tipped a bottle of calcium and had a massive shift in PH (I had to put him in my emergency tank, because I had to drain my show tank). But beware they are also very nasty and are very territorial, and may need to be taken out and given back to the pet store later when you add more fish. ( I had to do that because they bullied my onyx clowns)
Make sure you cycle for at least 3 weeks with live rock before you add any livestock. I also recommend you add 3-4 damsels and wait a week before you add anything else
IMPORTANT LAST NOTE: make sure you do your research on everything you buy, saltwater stuff isnít cheap at all, the average tank can cost hundereds if not thousands of dollars to setup, also donít try a small nano tank first, try a larger tank, the larger the tank the less capacity it will have to crash because of salinity swings and chemical imbalances in the nitrogen cycle. Plus smaller tanks are much harder to take care of. Please research this stuff for about a month before considering a saltwater tank, it will save you much money in the long run.