Best thing to do, IMO
, is save the money. Before you holler out and yell in protest let me explain.
1. Books will be among your most important investment, among them The New Marine Aquarium by Michael Paletta and The Consciencist Marine Aquarist by Robert Fenner. Buy used if you can but this $40 investment will save you a ton of money in the long run.
2. Research. What is it that you ultimately want? A FOWLR
aquarium may be more satisfying but, if you are looking to spend all $200 now, know a FO
is the way you will go. A reef aquarium can be extremely expensive. As an example, I spent $92.50 for 15 lbs of live rock and another $75 on the power compact lights. All that on a 10G tank that cost me $6. Hard to believe the tank itself can be among the least expensive things you buy for a saltwater aquarium setup.
3. Be patient as saltwater, especially reef, tanks never are quick and easy. Lots of patience is required but the end result will be worth it.
That all being said, for the 20 you have you will need: a hydrometer, some test kits, 3 powerheads (two for the tank), 2 heaters (one for the tank), the salt itself, 2 thermometers, 2 5G buckets, water, sand, lights, and siphon hose will run you roughly $185. May be able to pick up a damsel or two with what is left. This leaves you with a tank that has fish in it with a sandy bottom and no live rock. However, you will be able to do water changes. Forgot the surge protector that will run an extra $10.
Take your time and save the money until you finish reading the books (which were not included in the above initial costs). By far that will be the best thing you can do.