Super interesting, it looks to be the same. I used 50% RODI water, with a pinch of red sea blue bucket salt.Can we have a full pic of the tank and a pic of the sump if it’s got one. Looking on the bright side, at 0.8, it ain’t going up. Can you make a glass with 50% new salt water and 50% tank water, then test that see if you get 0.4 ish (just to evidence it’s a real reading and not a dodgy test kit, method).