Specific Gravity (SG) -LiveAquaria.com Suggested Reef Aquarium 1.023 - 1.025 -ReefKeeping.com Suggested Reef Aquarium 1.026 -LiveAquaria.com Suggested FOWLR Aquarium 1.020 - 1.025 -Natural Reef 1.025-1.026 Poll Question: What SG level do you target and why?? Second question: If you measure your SG and it is too low or too high, what procedure do you use to adjust it? If too low, suggest doing what?.... How? add salt to sump or Water change with higher salinity water? How do you determine how much salt to add? If SG too high, suggest doing what?.... water change and adding RO/DI instead of salt water?? How do you to determine how much water to remove and how much RO/DI to replace? If mine is low, I have been adding small amounts of salt to my sump every few hours to gradually raise it. Roughly 1/2 cup per hour for a 75 gal total water volume system until 1.024 is reached. If it is too high, I take some water out and replace with RO/DI every few hours to gradually reduce it. Roughly 1/2 gal salt water removed and 1/2 gal RO/DI replaced every hour for a 75 gal total water volume system until 1.024 is reached. Final question: I use a refractometer to measure salinity. Hydrometer based SG measurement are too imprecise for these measurements based on my research. Alternative would be a digital probe of some kind at additional expense. Any better ways of doing this??