RO water is a must. Many many patients, salt tanks are slow going so don't rush them or you will likely fail. Any failed salt experience is expansive compared to fresh. You will need a reef test kit, salinity tester, plus the ammonia test as well. Fish just can't be added, they need to me acclimated to your water so research and ask you local fish store for help with this very important step. Mix your salt solution a couple days before you are ready to change water. Be sure to have lots of live rock, like 20 pounds or better. Read and research every fish/invertebrate before you buy for compatibility. These are just a few musts, I am sure others will have more.