It is best to use RO
water. It is not "cycled" water. Tanks get cycled, but it is not the water that is growing the good bacteria during the cycling process, it is being grown on surfaces such as rock, sand, filtration media and things like that.
You mix the saltwater in a bucket, rubbermaid container or whatever you have that is large enough to hold the water that you will be using. Let it mix well and aerate for 24 hours before using. During the cold months, you may want to put a heater in there to make sure the water is the proper temperature. If you are using a quality salt mix, additives are not needed.