Specific Gravity
SGWhat does Specific Gravity mean?
Specific Gravity (SG) is the density of saltwater relative to pure water at a fixed temperature. Aquarists use SG as a proxy for salinity in reef + saltwater tanks.
How is Specific Gravity used in aquariums?
Reef tanks target 1.025-1.026 SG (corresponds to ~35 ppt salinity). Use a refractometer (NOT a hydrometer - hydrometers drift 1-3% within a year). Calibrate refractometer with 35 ppt calibration solution monthly.
How Specific Gravity fits the bigger picture
Understanding Specific Gravity matters because it's connected to broader husbandry decisions: water chemistry is the foundation of every other aquarium parameter - chemistry mistakes show up months later as livestock loss.
Browse the Fast Aquatics care library for full husbandry tutorials covering Specific Gravity in context.
Frequently asked questions
What does Specific Gravity mean in fishkeeping?
Specific Gravity (SG) is the density of saltwater relative to pure water at a fixed temperature. Aquarists use SG as a proxy for salinity in reef + saltwater tanks. Reef tanks target 1.025-1.026 SG (corresponds to ~35 ppt salinity). Calibrate refractometer with 35 ppt calibration solution monthly. Understanding Specific Gravity matters because it's connected to broader husbandry decisions: water chemistry is the foundation of every other aquarium parameter - chemistry mistakes show up months later as livestock loss.