Need
*Water - purified, rodi is best
*Salt
*Flow - 30-100 gph times the size of the tank (like a 10g needs at least 300 gph in powerheads)
*Light
*Heater and maybe chiller
*Someplace for bacteria to live - at least 2/3# rock per gallon of water
*Test kits - ammonia, nitrate, alkalinity, calcium, magnesium, phosphate, salinity, temperature
*Quarantine and a set of common meds / nutritional supplements
Optional, but nice
Auto top off
Skimmer
Sump
Gfo
Dosing rig for supplements or carbon; or kalk
Personal choice
Sand
Mechanical filtration - filter socks, canister filter, floss pads etc.
Nutrient removing algae - turf scrubber, chaeto etc.
Granular activated carbon
Gravel vacuum