Review on Saltwater Aquarium Seawater | Salinity 0.95-1.08 by Tres Carmon

I use this to measure my girlfriend's blood salt level for home hemodialysis and I get a PPM reading that is about 1000ppm lower than their lab results on the same day. I've tried recalibrating it, but judging by the damage it only allows you to go up to 20% higher than it's factory calibrated. It says if the calibration is off by more than 20% (which I can't guarantee, it's not because I'm measuring blood and not pure pool water) it should be replaced. Well I just received this item and doubt it will need replacing any time soon so maybe it's my fault. However, it doesn't read blood properly, so don't try it. So 3 stars I think? I don't want to be too negative, but I can't be too positive either.