Bigger is better when you're starting out. If you don't understand what they're talking about then you're probably not ready for a nano reef. Going into it without knowing anything about tank maintenance will cost you a ton of money in the long run, not to mention a lot of disappointment. At least give yourself some more time to do research before you start buying.
I could not possibly imagine setting up a reef tank from scratch with just $120. You could *maybe* do a fish-only or fish only with live rock. A freshwater setup could be done pretty easily with that kind of money though.
But here's a list for a 10g fish-only, at a minimum:
Tank w/canopy and light hood (no stand necessary. a sturdy table will be ok) ($30 with the top)
Bag of aragonite sand ($25)
Salt Mix ($10), distilled water (2.00/gal
) and hydrometer ($8 ) (your LFS
may have RO
and/or pre-mixed salt water)
Master Liquid Reagent Test Kit ($20)
Protein Skimmer and/or filter ($120 for skimmer)
50watt heater ($15)
So you're already at $220 here.
To go reef, you'll also need:
20-30 lbs live rock (usually $7.00/lb)
For most corals, you'll need to upgrade your lighting to at least 3 watts/gallon - the lights that come with a tank are usually about half that. (my 3.2wpg compact flourescent lights were $60)
So a reef would be about $400, at least
Did I miss anything? I just recently set up a reef myself so there might be something I'm forgetting
Keep in mind also that SW
fish and corals can be relatively expensive as well. Also, your fish choices would be limited: