The definitive Am I Cycled...how to.
 

It's real easy to miss the ammonia spike entirely and be left wondering, am I or am I not?

There's also an easy test. Drop a tiny pinch of ordinary fishfood into the tank every day. (I actually just start this way, and cycle in about 4 weeks.) Continue to drop the fishfood into the tank. If you still don't see ammonia---in your daily check---the cycle very likely sneaked past you. You MIGHT be cycled.

But just to be safe, start off not with a fish or coral, but with a tiny cleaning crew, couple of snails (NOT margaritas: they die in warm water) ---and a couple of micro hermits: scarlets are the best. I have one that's at least 5 years old and still going. They're fairly tolerant of problems. If they thrive (keep adding that fishfood daily: they have to eat, and your tank is too young to feed them yet)---you can start your first fish in quarantine---(Why not put it on in? BIG reason. If it brought ich, ich spends 3/4 of its life not on fish but in sandbeds. You do not want that nice new sandbed infested with ich. So be double and triple sure your first fish is ich-free, and free of other nastiness, too. Familiarize yourself with (google the pix) ich, fin rot, lymphocystis, and gill flukes, for starters.

When buying that fish, look at how the water is piped inside your fish store. Do not buy from a tank with sick fish or from any tank connected to that tank via a common sump. Do not buy a fish with flaring gills, (fluke or ich) or one being picked on by others. A pity-buy can be real expensive. Leave the sad cases for an expert. And remember, if you're in love with a particular fish, there WILL be another of that species eventually. Talk to the store owner, make a request. It may be seasonal availability, but it will come around again. Buy only when you're ready; and remember, the word 'rare' means 'it doesn't last long' and certainly won't in the hands of a novice. You are BOUND to make a few mistakes with water salinity and quality before you get the hang of it all. Pick species that are fairly hardy, and for gosh sake---ask to see the fish book (there's a big one that most stores have for reference) and look up or just ASK the adult size of the fish. 'Dory' grows up to a foot long. A naso tang gets to be a foot and a half. And no, tank size does not limit their growth.
Happy reefing.

Also: invest in an autotopoff early. There will come a day even for a nano-nano that you have to be gone for 3 days and can't top off by hand; and if you're toward 50 gallons you're apt to evaporate a gallon a day, which is way too much to be doing by hand. Evaporation is not a bad thing: it's a good thing if you're aiming at stony coral or clams, (because you can use it to drive a calcium additive into your tank along with your fresh water.) But with that kind of water evaporation you're either going to spend your life testing and topping off to keep your salinity steady, or you get an autotopoff unit that will automatically suck fresh water from a bucket (I use a 32 gallon barrel) and keep 'making up' that freshwater loss evaporation causes. ALways remember: water evaporates: salt doesn't. If you don't top-off daily, your relative amounts of water and salt are going to go off and off and off.