Red Sea Seawater Refractometer
Water type
Marine
Test range
Up to 40 ppt
Test method
Refractometer
Scales
SG and ppt
Temp compensation
Automatic, 25°C ref
Includes
Pipette, screwdriver
Red Sea Seawater Refractometer
One accurate salinity reading is worth more than a dozen rough ones. The Red Sea Seawater Refractometer is calibrated specifically for seawater rather than fresh water or brine, with automatic temperature compensation (ATC) built in, so a reading taken straight from the tank is close to true without needing the sample to reach a set temperature first.
Key features
- Seawater-specific calibration – a generic refractometer calibrated for brine or fresh water can read out by as much as 1.5 ppt on seawater; this one is built and calibrated for the job.
- Automatic temperature compensation – corrects for sample temperature against a 25°C reference, though letting the sample sit a few minutes to approach room temperature still gives the most reliable reading.
- Dual scale – reads specific gravity and salinity (ppt) side by side.
- A couple of drops is all it takes – no test tube to fill or colour change to wait on.
- Included calibration screwdriver and pipette – everything needed to zero the unit and take a sample is in the box.
Specifications
| Spec | Value |
|---|---|
| Measurement range | 1.010–1.030 specific gravity / 20–40 ppt salinity |
| Temperature compensation | Automatic (ATC), referenced to 25°C |
| Calibration method | Zero-point calibration against RO/DI water, adjusted with the included screwdriver |
| In the box | Refractometer, pipette, calibration screwdriver |
Suitable for, and not suitable for
Suitable for any marine or reef aquarium where salinity needs to be checked accurately – new water changes, top-offs, and dialling in a fresh salt mix. Not a substitute for a proper calibration routine: even with ATC, a refractometer calibrated weeks ago will drift, so re-zero it against RO/DI water regularly rather than trusting an old calibration.
Care and maintenance
Zero the unit against a drop of RO/DI water before each session, or at minimum every few weeks with regular use. Wipe the prism dry with a soft, lint-free cloth between readings – salt residue left to dry on the prism is the most common cause of a drifting reading. For the most repeatable results, calibrate against a 35 ppt reference fluid if you have one, rather than RO/DI water alone.
Warranty and delivery
Covered by your consumer guarantee rights under Australian Consumer Law. This is a small, well-packaged item that ships standard parcel post.
Common questions
Do I need this if I already have a hydrometer?
A swing-arm hydrometer is accurate enough for a fish-only tank but not for reef salinity, where small errors in calcium and alkalinity dosing compound over time. A refractometer reads more precisely and doesn't have moving parts to stick or wear.
Does it need calibration fluid to work?
No – it calibrates against plain RO/DI water for everyday use. A 35 ppt calibration fluid gives a more precise zero if you want to check it against a known reference occasionally.
How accurate is it?
Red Sea doesn't publish a numeric accuracy figure for this model. What it does state is that a seawater-specific calibration avoids the up to 1.5 ppt error seen when a generic (non-seawater) refractometer is used on saltwater.
Does it come with a carry case?
Not that we can confirm from Red Sea's own specifications – it ships with the refractometer, pipette and calibration screwdriver.
