$Salinity Meter or Refractometer$

Salinity Meter / Refractometer

Salinity Meter / Refractometer — helps with marine fish stress, coral disease.

Solves: Marine fish stress, coral disease
Best for: Saltwater aquariums
Price range: $80–$160

Recommended for these conditions

Roughly nine out of ten disease calls trace back to a water-quality slip you could have caught early. Salinity Meter / Refractometer turns invisible problems into a number you can act on.

Where it really pays for itself is marine fish stress, coral disease. That is the exact failure point behind several of the conditions in our library, so addressing it directly shortens treatment time and cuts re-infection.

How to use it well

Hyposalinity is a key treatment for marine parasites. Treat it as part of a protocol rather than a magic bullet — it works best alongside good husbandry and the medications matched to your specific diagnosis.

Conditions it helps with

On our disease pages you’ll see this equipment recommended for conditions such as:

Marine Ich
Marine Velvet
Amyloodinium

Who it’s for

Best suited to saltwater aquariums. Typical units run in the $15–$80 range, depending on capacity and features. Use the inquiry form below to ask about a specific model, request a recommendation for your system size, or get notified when stock and pricing are confirmed.

Care & Usage Tips

Calibration & First Use

Always calibrate with RODI water, never tap water
Tap water contains dissolved minerals that shift the refractive index. The refractometer should read exactly 1.000 SG or 0 ppt salinity with RODI or distilled water. Calibrate before every session in a new tank and at least weekly in active systems.
Use a temperature-compensating (ATC) refractometer for marine tanks
A non-ATC refractometer requires manual correction for water temperature. For marine fish health management and hyposalinity treatment protocols, ATC is not optional — temperature errors at these scales produce meaningfully wrong readings.
Apply only 2–3 drops to the prism — more distorts the reading
Excess water runs under the cover plate and creates an uneven film. The meniscus that forms with too much sample volume shifts the reading upward. A consistent, minimum-volume sample gives the most repeatable results.
Wait 60 seconds after applying the sample before reading
Thermal equilibration between the sample and the refractometer body takes about a minute. Reading immediately after application — especially if the sample came from a tank at a different temperature — will produce a transient, inaccurate reading.
Understand the difference between SG and salinity (ppt)
At 77°F (25°C), natural seawater is ~1.025 SG or ~35 ppt. For hyposalinity treatment of Marine Ich, target 1.009–1.011 SG (15–16 ppt). Know which scale your refractometer uses before dosing.

Accuracy & Care

Clean the prism with a lint-free cloth after every use
Salt crystals left on the prism between uses scratch the optical surface and progressively degrade reading accuracy. Rinse with a few drops of RODI water, then wipe with a lint-free optical cloth. Never use paper towels — they scratch optical glass.
Recalibrate monthly during active treatment
The set screw calibration on most analog refractometers can drift from vibration and thermal cycling. During a hyposalinity treatment course, recalibrate every 3–4 days to ensure you’re maintaining the therapeutic salinity window reliably.
Store with the cover plate open to prevent seal degradation
Leaving the cover plate closed traps moisture against the prism and the rubber seals. Open the cover plate and allow the prism to air-dry before storing the refractometer in its case.
Cross-check with a digital refractometer periodically
Analog refractometers can develop prism delamination or calibration screw drift. Cross-check with a second measurement method every 30 days if you are actively managing a hyposalinity treatment.
Replace the rubber eyepiece cover if it hardens or cracks
A cracked eyepiece cover allows moisture into the optics housing and can fog the internal prism. Replacement eyepiece covers are inexpensive and available from most optical supply vendors.

Frequently asked questions

What does Salinity Meter / Refractometer do?

The Salinity Meter / Refractometer helps control marine fish stress, coral disease — common triggers behind fish disease.

What conditions does Salinity Meter / Refractometer help with?

Salinity Meter / Refractometer is recommended for conditions such as Marine Ich (Cryptocaryon irritans) and Marine Velvet (Amyloodinium). Each linked disease page lists the full set of gear that helps.

Who is Salinity Meter / Refractometer for?

Salinity Meter / Refractometer is a good fit for saltwater aquariums. It works for both prevention and active treatment.

How much does Salinity Meter / Refractometer cost?

Salinity Meter / Refractometer typically costs in the $80–$160 range, depending on capacity, build quality, and features. Use the inquiry form on this page for a recommendation and current pricing.

How do you use Salinity Meter / Refractometer?

What should you know about Calibration & First Use?

Always calibrate with RODI water, never tap waterTap water contains dissolved minerals that shift the refractive index. The refractometer should read exactly 1.000 SG or 0 ppt salinity with RODI or distilled water. Calibrate before every session in a new tank and at least weekly in active systems.