i have a hydrometer that came with a tank i got. i have no use for it as i have turned the tank into freshwater and dont keep salty fish.... its an instant ocean hydrometer
http/www.fishtanksdirect.com/browseproducts/Sea-Test-Hydrometer.html
http/www.fishtanksdirect.com/browseproducts/Sea-Test-Hydrometer.html