Product overview
Salifert Refracto Check is a calibration fluid for marine salinity meters. Salinity is the baseline for the rest of your water chemistry. If a refractometer is aligned to pure freshwater (zero) instead of seawater, the scale can be wrong at tank salinity, so you may dose or mix salt to the wrong value. That can stall coral growth, cause osmotic shock, and fade colour.
The solution matches tropical seawater at 35 ppt / 1.026 SG. You put drops on the prism only — nothing goes in the tank.
Key features
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Seawater standard: 35 ppt (1.026 SG), close to typical reef targets.
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Not RO/DI zero: Calibrating the prism at 35 ppt avoids the linearity error you get from setting the scale with pure water.
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Bottle size: 10 mL, enough for about 100 calibrations.
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Speed: Re-zero most optical instruments in under two minutes.
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Off-tank: Used only on the device prism, so it does not enter the aquarium.
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Seal: Tight bottle to limit evaporation so the standard does not concentrate on the shelf.
Water and system compatibility
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Water: Marine and reef use only. Not for freshwater hydrometers or planted tanks.
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Devices: Handheld optical refractometers, digital refractometers, and ATC salinity sensors.
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Routine: Check the instrument before mixing salt or reading other chemistry so salinity error does not throw off calcium, alkalinity, or magnesium dosing.
Calibration and instructions
Always follow dosage & directions on product packaging.
Aim for a stable 35 ppt / 1.026 SG system baseline unless your livestock requires otherwise. When to check:
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Routine: Recalibrate at least once a month to offset lens or thermal shift.
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Water changes: Check the meter just before mixing a new batch of salt.
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Odd readings: Calibrate first if calcium, alkalinity, or magnesium seem to have dropped without a clear cause.
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Before use: Shake well, clear dried salt from the nozzle, and discard the first 3 drops so you are not using stale fluid. Then cover the prism.
Storage
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Cap: Seal immediately. Evaporation raises the salinity of what is left in the bottle. Do not leave the dropper loose between drops.
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Location: Dark cupboard at room temperature. Do not freeze or overheat.
Specifications
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Brand: Salifert
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Range: Testing instruments and accessories
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Volume: 10 mL
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Target: 35 ppt / 1.026 specific gravity
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Use: Approx. 100 calibrations per bottle
