The Hugo Kamishi Hydrometer / Thermometer is the same type of hydrometer which comes pre-packed with the current-generation Cubic Orbit 20 Desktop Jellyfish Tank.
This hydrometer works by being floated into the tank.
The green strip on the Hugo Kamishi Hydrometer is indicative of whether the water salinity is correct or not.
The surface of your jellyfish tank’s water should be level with the green mark to ensure your water is at correct salinity for the safe-keeping of jellyfish.
This hydrometer also doubles up as a traditional thermometer, to ensure you’re keeping on top of water temperature, too.