Originally Posted by lousieg55

okay, so, I will be getting another 5 gallon eclipse, So I all ready have one 5 gallon fresh and a 29 gallon fresh. Figure i might try salt with this one.

I wouldn't recommend starting off with SW in a 5 gallon tank. You'll be very limited in options for what you can keep, but more importantly, small tanks are difficult to keep stable compared to larger tanks. I started off in a 2.5 gallon and I had to top it off twice a day for evaporation. Small tanks need a ton of attention and if anything goes wrong, it will happen very quickly.

Couple questions,

1. 5 gallon to small(what fish can live in 5 gallon) Same 1 inch per gallon rule apply
The inch per gallon rule is bunk even for FW, but really doesn't ever apply for SW. The only fish I'd recommend keeping in a 5 gallon would be a clown goby, as they are stationary much of the time.
2. Do i need corral or live plants or both.
You don't need either, but if you decide later that you want to keep coral, you will need to upgrade the lighting. I don't know how you would even go about that in a 5 gallon Eclipse due to the top-mounted filtration and lack of space in the hood, but the lighting that is included is woefully inadequate for coral.
3. Sand or rock?
I'd go for aragonite sand substrate and some live rock for bio filtration purposes.
4. Whats diffrent from fresh to salt
Tons. I'd suggest doing a TON of research before you jump into a SW tank. There is a lot of bogus information out there, and a lot of equipment, and researching will better prepare you to be successful as well as save you money in the long run. Check out Fenner's "The conscientious marine aquarist."
5. Do you still need air stones
No.
6. Anything i need to know.
I'd suggest buying a refractometer so you can monitor the specific gravity of your water. For a reef tank, I'd keep SG at 1.024-1.026; for fish only you can keep it a little lower. You'll need marine salt mix to make SW (aquarium salt won't do it). You'll need to top off with fresh water to compensate for evaporation- the salt does not evaporate and the SG will rise because of evaporation. It's highly recommended that you use RO/DI water for water changes and top offs.
7. Does the bio spira instant ocean work
Even if it does, I wouldn't use it. You can cycle the tank with your live rock and either a raw shrimp or pure ammonia. If you have enough die-off on the rock, that can get your cycle started in and of itself. More importantly, there is a big difference between completing your cycle and having a stable tank. SW tanks take months at a mimimum to start to mature. Our latest SW tank has been running for over 6 months and I still wouldn't call it "mature."

KK so i know about fresh water the basics, I have no idea about salt. Thanks louis.
If you definitely want to keep a small tank, I think the easiest setup would be an all-in-one tank like the Biocube, nanocube, or Aquapod. They range in size from 6 gallons to 29 gallons and are pretty reasonably priced. The lighting that is included is adequate for many soft corals and some LPS (long-polyped stony) corals. I kept a Biocube 8 gallon for some time, and once I replaced the stock pump and exchanged the bio balls for live rock rubble.