Hi,
Welcome to the site!
Just setting up, or has this tank been going for a while? Do you plan on corals (reef) as Mr. limpid asked, or fish only with live rock (FOWLR)
2 power heads are needed equipment...Do you have those? How much live rock? What kind of substrate? What type of filter? What kind of lighting? What type of test kit do you have?
A UV sterilizer kills the good critters and the bad. The little copepods the fish love to eat comes out at night, so if you have a UV sterilizer, you would need to shut it off at night. Like Mr. Limpid said...waste of money. A skimmer isn't really needed, if at all, for about 2 to 3 months after fish are added. Octopus, Tunze and Aquaticlife are decent skimmers. If you don't have a refugium or macroalgae, I do recommend a skimmer...but like I said...2 to 3 months down the road.
What you need to focus on if you have just set it up...would be your quarantine tank.
10g to 20g tank (regular fish lights)
No sand
No live rock
An air line (no stone) attached via rubberband to a piece of PVC pipe or resin decoration. (the resin décor can be removed if you have to treat the new fish if it's infected with parasites, or sick). A piece of PVC will give the fish a place to hide and make it feel secure...macroalgae will help stabilize the tanks parameters, and add oxygen and make the fish happier.
A little over flow filter (Whisper or penguin type)
Toss in a piece of shrimp to kick start the cycle (do not cycle with a live fish) . When it's ready (ammonia spikes, then drops to 0, Nitrites read 0 and you see nitrates) Then add 1 fish...watch it for 3 to 4 weeks and when you are sure it doesn't have parasites or is sick...then add it to the 55g display, and you will be ready to add another fish...just 1...to the QT. That will keep the display healthy, and help you regulate the space of time to add new critters, thus avoiding the "too much too soon" crash.