As best combination among accuracy and good usability I recommend:
- hydrometer with good quality measuring in „density “, not „specific density“ (e.g. Tropic Marin, JBL)
- Thermometer with an accuracy of 0,1 °C/°F (needed to measure water temperature together density!)
- Measuring cylinder from glass or plastic (tall / slim, 500ml) (gather tank water and measure within this device, instead of measuring in the tank!)
Second best choice is a high quality refrak, which must be calibrated for salt water (not NaCl !).
(Read the salinity in [psu] from this device instead reading the „specific density“ which is also shown by most of this devices).
Refraks should be calibrated with salt water of an “exactly know salinity” within the range that should be measured
(best: use a reference solution!).
Calibrating with distilled/RO-water is not suggested
Advantage of this tool:
- Only 1, small tool needed
Disadvantage:
- Measured value are not too accurate due to small scale which is hard to read
- Calibration with RO-water recommended before each use
Less recommendable are:
- pointer hygrometers (get crusted pretty fast and thus might show wrong results, temperature measurement also needed)
- Conductance sensors (expensive, must be calibrated, temperature measurement also needed)