What I do when setting up my quarantine tank.
It takes a little pre-planning.
I take a air powered sponge filter ( 6" x 6" ) and put it in the sump of my display tank for 5-6 weeks to seed it.
Then I just set up the 20 gallon tank. Add fresh saltwater. ( why not add the best possible water) I use a small back filter, and a small powerhead, and heater. A ammonia alert badge can be useful.
I use pvc fittings or other plastic tank decorations for cover for the fish.
I use a small freshwater light hood.
I usually pre-order live foods like tigger pods or live brine to help get newly shipped fish eating.
I plan on doing at least 30 days of copper once the fish is eating and settled in.
Then 2 rounds of prazipro.
The last year or so I skipped this and just bought fully quarantined fish from Dr. Reef. Saves me the stress of all this.