A refractometer is used in aquariums to measure the water's salinity by detecting how much light bends as it passes through a sample. It displays salinity in parts per thousand (ppt). These tools are most commonly in use in marine aquariums, but can also be handy for freshwater aquariums when undergoing a salt treatment. Features Measure salt concentration accurately during a salt treatment. Confirm therapeutic doses if you're treating fish over several days and doing water changes. Avoid overdosing or underdosing, especially in valuable or sensitive fish. High definition eyepiece give your a broader view and make your can read more accurately. Includes custom protective carrying case, pipette and a mini-screwdriver for easy calibration. Widely used in mariculture and saline solution preparation, Measurement range: 0-100% salinity Accuracy: 0.001sg(1%) Salinity Proportion: 1.000-1.070sg Size: 19.4 cm Some aquarium plants may be sensitive to salt treatments, it may be necessary to transfer fish to a hospital tank in the case of a planted aquaria Aquarium salt (pure sodium chloride without additives) can help treat certain freshwater fish health problems and may be beneficial for: Mild external parasites (depending on the species) Minor bacterial or fungal infections (as supportive care) Nitrite poisoning, where chloride ions reduce nitrite uptake by the fish Reducing osmotic stress, making it easier for damaged fish to regulate fluids Treatment concentrations: 0.1% (1 g/L): Mild supportive treatment. 0.3% (3 g/L): Often used for stronger parasite treatment, if the fish species can tolerate it.