You can calibrate your cheaper hydrometers to a good one, like if your LFS where you spend $ has one. Take yours in.
cheap hydrometers aren't calibrated for squat, but they are repeatable, so they take to a re-scaling just fine and then are quite accurate. make great backups too.
LR is tough stuff, relatively speaking. Also, it has probably been shipped nearly dry a couple of times (ie wet papr towels etc), stored in a holding location for curing, warmed, cooled etc
so, it will be super happy being in anything resembling ocean water once again. Once your LR has established its bacteria colonies after some months, then maybe a salinity shock could wipe out some of the bacteria/coralline/small marine life that has survived or repopulated
massive changes in salinity can explode or collapse cells if they can't handle the osmotic pressure. This effect usually is more drastic, the smaller and simpler the life is. This is why fish can take a fresh water dip, but the little micro-parasites can't. Or the ends blow out of caulerpa that gets thrown from one salinity into a fairly different one.
Go slow, get good feedback equipment (test kits, meters,etc)
and read read read read read
Anybody still read Borneman's coral book?