Starting a small saltwater tank?

What do you want to put in there? How much attention can you provide daily?

There are 2 main problems with small SW tanks. 1. Salinity and other parameters varies more in small tanks. A little evaporation, and you can suddenly have a lethal stew. Stabilizing small tanks requires daily attention for the first 3-4 months until you're established a routine. 2. There are very few fish that will survive in a small tank. Gobies, a few wrasses, and possibly a percula or ocellaris clown are about it--and you'll only wna tto have 1 or 2. Inverts and corals are better choices--but only once the tank has been kept stable for a while.

Small tanks require more patience!

Even then, I wouldn't encourage anyone to setup anything less than about a 30 as their first marine tank.

I've been keeping a 2.5g saltwater for about a month now (Far short of the time period needed to call it a success). It has 2lbs of live sand, 2lbs of live rock (well cured in lfs and brought home in bucket of saltwater to avoid dieoff). A very small internal canister type filter (came with betta kit), a red-sea mixing pump and the liverock are the only filtration. I have to top-off DAILY in order to maintain salinity, and a 20% water change is done weekly. It is stocked with a couple hermit crabs, a clown gobie, and some of the smallest polyp frags you've ever seen. Lighting is from the a 12w "screw-in" CF. It can be done, but it's takes alot more attention than a larger tank. They're called Pico-tanks, and they are growing in popularity. I consider mine more of an experiment in progress than anything else.

There are lots of possibilities for inverts, as OG said.

For corals, you would do best with the easiest varieties, since you are just starting out. Mushrooms (corallimorpharians) and "polyps" (zoanthids) are quite hardy, and won't outgrow a small tank. Star polyps, a group of mat-forming soft coral, will also be good. They are usually inexpensive, as corals go, and online vendors often have "nano packs" of hardy corals.

Peppermint shrimp are also easy to care for, and can be had for $6-$10, depending on the source. Skunk cleaner shrimp are more attractive and outgoing, but can be about 2-3 times as expensive. A pair of either will work in a nano of reasonable size. Hermit crabs can be very interesting, and make good cleaners, but get non-aggressive species like scarlet reef hermits. Small snail species, like ceriths and nerites are good for algae control, as well as slightly larger species, such as Astraeas. Turbos and trochus will get too big.

Fish? My preference is to avoid fish in any tank smaller than 10 gallons, but small species like neon or clown gobies will do allright.

I would depend mostly on the live rock/sand for filtration. Lighting will depend on the corals you want to keep.

A good heater, a counter current skimmer (you like to take care of things right? ), Coralife makes a 50/50 screw-in retrofit PC bulb I believe it's 20w I'd use that. Then figure out what you want, think inverts like mushrooms, hermits, and other indestructible animals. Gte the tank setup first. That being said I'm with Oriongirl 30gal or at least 20gal would be alot easier and allow you to actually keep some fish.

Gobie and pistol shrimp are pretty cool (they form a symbiosis). i have them in a 10G they will need sand to make a home and live rock always helps

Stability

I really would think about saving or selling that tank and putting towards a bigger though, stability on that size tank will be up and down something cronic! maintenance will be needed daily without a miss! and remember stress and disese is so easy to develop in marine and in a small tank thats deadly! Have a go but your might find its just to much maintance and wish after all the cycling ETC you had gone for a slightly bigger tank which will be a happier living for fish and easier maintenence.

Gib