The only thing i will offer at this time is go with a refractometer, which can easily be adjusted if calibration is off, and easy to clean since nothing gets inside. If a hydrometer isnt cleaned well right after use it can get build up on the float and wont be accurate. Either instrument needs to be checked for accuracy!
The difference in price is about the cost of 1 filter or a couple water changes.
The difference in price is about the cost of 1 filter or a couple water changes.

