Hi, Welcome to the site. Yep, get a good beginners book.
If you don't have live rock, you will need to seed the fake coral with the tiny critters needed to keep your SW tank balanced. You get those critters free on rock, but one way or another, you need them.
You can use black sand, but it shows all the yuck on the sand, and it tends to fade to gray over time.
A 55g is a very tiny SW water tank, figure 5 fish that can get along together. EXAMPLE: A pigmy angelfish, a goby and maybe a few firefish and a Royal Gramma. You will need snails, a meat eater to eat the wasted food in the rock/or fake coral...such a brittle starfish or serpent star. A few shrimp too.
Unlike freshwater tanks, the cleaning up crew (CUC) critters for SW really do their job.
- SW has less oxygen, so you need a few power heads to circulate the water (the wave is life of the ocean, and your SW tank)
- A skimmer (you won't need it right away, give it a few months)
- Salt mix
- RO (reverse osmosis) water is a must, RO/DI even better... if you can't get your own unit, go to a water refill station at the grocery store, but whatever you do...don't use tap water.
- You need a mixing bucket, and a storage for clean SW (I use a plastic garbage can) a utility pump to keep the water moving in the storage, and stir the salt to help it mix for 24 hours before use.
- Extra flex hose to help with water changes. attach the hose to the utility pump to remove and then replace water. (saves your back)
- Hydrometer or refractometer... the refractometer is more accurate.
- Your own lab type test kits, not strips.
- For looks...a canopy and a background. SW tanks should be open, so no lid... a canopy gives the illusion of a top, and makes the tank look so much nicer. The background hides all the wires in the back and really makes the tank look good.