Free reef tank tool
Reef Salinity Converter
Convert specific gravity to ppt, ppt to specific gravity, and check whether your salinity is in a common reef tank range.
Static reef salinity chart
Reef Salinity SG to PPT Chart
Approximate reef hobby conversion at around 25°C / 77°F. Actual readings depend on temperature, calibration and instrument type. This chart is approximate. Specific gravity readings depend on temperature, hydrometer/refractometer calibration and instrument type.
| PPT | Approx. specific gravity | Range note |
|---|---|---|
| 30 ppt | 1.0226 | Low for many reef tanks |
| 31 ppt | 1.0234 | Low for many reef tanks |
| 32 ppt | 1.0241 | Slightly low |
| 33 ppt | 1.0249 | Slightly low |
| 34 ppt | 1.0256 | Common reef range |
| 35 ppt | 1.0264 | Common reef range |
| 36 ppt | 1.0271 | Common reef range |
| 37 ppt | 1.0279 | Slightly high |
| 38 ppt | 1.0286 | Slightly high |
| 39 ppt | 1.0294 | High for many reef tanks |
| 40 ppt | 1.0301 | High for many reef tanks |
How the Reef Salinity Converter Works
This reef salinity converter estimates between ppt and specific gravity for saltwater aquarium planning. It uses a small reef hobby conversion table for the common 30 to 40 ppt range and a simple fallback approximation outside that range. The goal is to make common conversions easy, such as 35 ppt to specific gravity, 1.026 to ppt, or 1.025 to ppt.
Treat every result as an approximate aquarium salinity converter, not a definitive instrument reading. Specific gravity is affected by temperature, calibration fluid, hydrometer or refractometer design, and how cleanly the sample is measured. If a result would lead to a major salinity adjustment, re-test before changing the tank.
SG vs PPT: What Is the Difference?
PPT means parts per thousand and expresses salinity as a direct concentration-style value. Specific gravity compares the density of the saltwater sample to water, so the number depends on measurement conditions. Reef hobbyists use both systems, which is why an SG to PPT converter and PPT to SG converter are useful when comparing equipment, salt mix labels, online guides, and local fish store advice.
PPT is often easier to compare across reef references because a value like 35 ppt is clear. A reef tank specific gravity reading such as 1.026 is still useful, but it should be interpreted with the calibration assumptions of the instrument.
What Salinity Should a Reef Tank Be?
Many reef aquariums are kept around 35 ppt, or about 1.026 specific gravity in common reef hobby charts. A common reef range is roughly 34 to 36 ppt. Some systems run slightly lower or higher for specific livestock or maintenance reasons, so this converter labels the range instead of claiming one ideal number.
Stability matters more than chasing tiny differences. If your tank is stable and the measurement is near the common reef range, avoid making rapid changes just to match a chart. Watch livestock, verify the tool, and make corrections gradually.
Why 35 PPT Is Around 1.026 Specific Gravity
The reef tank salinity chart on this page uses approximate reef hobby values around 25°C / 77°F. In that table, 35 ppt maps to about 1.0264 SG. Other salinity ppt vs SG charts may show slightly different numbers because they use different temperature assumptions, rounding, or seawater density references.
That is why this page labels SG conversion as approximate. Small differences between 1.026, 1.0264 and nearby values are normal in hobby use, especially when different tools are involved.
How to Measure Salinity More Reliably
Use a refractometer or digital salinity meter that is appropriate for aquarium use, then calibrate it near the range you care about. For reef salinity, 35 ppt calibration solution is usually better than RO/DI calibration because it checks the instrument close to the target value. Rinse and dry the instrument after use, keep calibration fluid clean, and re-check if a reading looks unusual.
Match temperature assumptions when possible and give mixed saltwater time to dissolve fully before measuring. If a reading would cause a large correction, take a second sample before acting.
How to Adjust Salinity Safely
Avoid rapid salinity changes. In a mixing container, you can raise salinity by adding salt mix gradually, mixing fully, then re-testing. To lower salinity, add RO/DI water gradually and re-test. In a stocked display tank, do not add dry salt directly to the aquarium.
For stocked tanks, raise salinity through prepared replacement water or gradual water changes. Lower salinity with careful RO/DI top-off strategy or lower-salinity water changes. Fish, corals and invertebrates can react poorly to sudden swings, so slow correction and repeated measurement are safer than one large adjustment.
Setting Up a Reef Tank? Coral Choice Comes Next
Once salinity is stable, coral identification and care requirements become the next decision. Different corals need different light, flow, spacing, feeding, aggression buffers, and stability. Coral Identifier can help you scan coral photos and get likely matches before buying, placing, or changing care for an unknown coral.
Related reef tools
Plan salinity, then plan coral care.
Use these reef tools after checking salinity to plan salt mix, placement, light, flow, compatibility, and coral care.
Coral Identifier
Identify corals after the tank is stable.
Salinity stability is one reef setup step. Coral Identifier helps when you need likely photo-based matches before buying an unknown frag or changing light, flow, or placement.
Coral Identifier gives likely coral matches from photos, not guaranteed IDs. Use the result as a starting point and verify with trusted references before making care decisions.
Reef Salinity Converter FAQ
What is 35 ppt in specific gravity?
In common reef hobby references, 35 ppt is approximately around 1.0264 specific gravity at about 25°C / 77°F. Treat this as an estimate because SG readings depend on temperature, calibration and instrument type.
What is 1.026 specific gravity in ppt?
A 1.026 SG reading is roughly around 34.5 to 35 ppt in this reef hobby converter. Different charts and instruments may show slightly different values.
Is 1.025 good for a reef tank?
1.025 SG is often slightly below the common 35 ppt target but may still sit near many reef hobby ranges. Verify the reading with a calibrated instrument and avoid chasing tiny differences.
Is 1.026 the same as 35 ppt?
It is close, but not exactly the same in every context. 35 ppt is often shown near 1.026 to 1.0264 SG, while real readings depend on calibration, temperature and the instrument being used.
Why do SG and ppt not match exactly on my refractometer?
Refractometer calibration, automatic temperature compensation, residue on the prism, sample temperature, and calibration fluid can all affect the reading. A 35 ppt reference solution is usually better than RO/DI calibration for reef salinity.
Should I measure reef salinity in SG or ppt?
Both are common in reef keeping. PPT is often easier to compare across references, while SG is common on hobby hydrometers and refractometers. The important part is using a calibrated instrument consistently.
What is the best salinity for a reef tank?
Many reef tanks are kept around 35 ppt, roughly about 1.026 SG, with a common range around 34 to 36 ppt. Livestock needs vary, and stable readings matter more than chasing tiny differences.
Can I add salt directly to my aquarium to raise SG?
Do not add dry salt directly to a stocked aquarium. Raise salinity gradually with prepared replacement water or water changes, then re-test after each adjustment.
How do I lower salinity safely?
Lower salinity gradually with RO/DI top-off strategy or lower-salinity water changes. Avoid rapid drops, especially in stocked tanks with fish, corals and invertebrates.
How accurate is this salinity converter?
This salinity converter is a practical reef hobby estimate, not a laboratory calculation. Use it for planning and always verify important salinity changes with a calibrated refractometer or salinity meter.
Does temperature affect specific gravity?
Yes. Specific gravity is a density comparison, so temperature and calibration assumptions affect readings. ATC instruments help, but they still need correct calibration and clean measurement technique.
Should I calibrate my refractometer with RO/DI or 35 ppt solution?
For reef salinity, 35 ppt calibration solution is usually better than RO/DI calibration because it calibrates near the range you actually use. Follow the instrument instructions and keep calibration fluid clean.
More coral setup reading