With a new saltwater setup, make sure the salt is dissolved completely before adding any sand. When salt has not dissolved in your aquarium and sinks into your tank it will give you a false low salinity. The salinity should be anywhere from 1.020 to 1.025 and be fine for most organisms.
All salt mixes should be used in their entirety, as the different grains and minerals separate slightly during shipping. The portion in the top of the bag may not be the same as the bottom of the bag. Be sure to check the manufacturer’s instructions.
As far as adding any fish to your saltwater aquarium, drop your fish in a separate container for 1 to 1 ½ hour with a slow drip of the water in your aquarium, careful not to overflow your container. Also, make sure the temperature does not fluctuate. Although it is a good idea to have a hospital tank for your fish.
For brackish water, the set-up of a brackish aquarium is the same way you would treat a salt tank except you would use less salt. You usually want the specific gravity in a brackish water tank to be anywhere from about 1.005 to 1.015 grams per milliliter.