Remove the amount of aquarium water you wish to change and replace it with seawater. To maintain a healthy aquarium, change 10% of the water weekly of 25% monthly. For new aquariums that are 100% seawater, run filters for at least 30 minutes before adding fish or corals to allow the seawater to equilibrate and reach room temperature. Be sure to test the salinity of your aquarium water before a water change to correct for freshwater evaporation. If your salinity is too high, add purified or deionized freshwater until the salinity reaches the proper range (specific gravity of 1.022-1.025).