I have had the same hydrometer forever, and just bought a refractometer from red sea to try hypo. Luckily I think I have flukes instead of ich. But this expensive refractometer is constantly off calibration, is tempermental, and just plain sucks! After watching videos on youtube, it seems many expensive refractometers read a few ppt off consistantly. So I did a test on my old 10$ hydrometer. It reads 1.000 in ro/di water and 35 ppt in solution. Now why does everybody say just dont use a hydrometer for hypo? Is there any reason not to use one that is working correctly? What am I missing, these expensive refractometers don’t seem to be all that great. My hydrometer has read 1.025 in my aquarium every time I have ever tested it (I have autotopoff). I’ve owned this refractometer for 2 days and it gives me a new number every single time.