[header] How to mix saltwater for an aquarium [title] Buy a sea salt mix. [step] Fish supply stores offer two ways to get saltwater for your aquarium. One is by pre-made saltwater or getting a synthetic sea salt mix that you blend into the water. 
If you plan to mix your own saltwater, make sure you purchase the pre-made saltwater solution that you add to water that you supply. [substeps] Get a dry synthetic saltwater mix.