Synthetic aquarium salt should be mixed with RO (Reverse Osmosis or RO/DI (Reverse Osmosis & Deionized) water. All of our synthetic salts contain calcium and trace elements that match natural ocean water, which will help to achieve the proper pH levels. However, over time you will need to replenish calcium and trace elements, and you may need to add buffers to help maintain ratios for proper pH balance. When doing water changes you will need to add more salt, but when only replenishing evaporated water, it will not be necessary to add salt, because the salt will not evaporate in significant amounts. Keep your salt containers well sealed as moisture will turn your salt to rock. All salts we carry are very high quality salts that are appropriate for reef aquariums as well as saltwater fish only tanks.