Just wanted to put in my 2 cents worth.
When ever I start a new bucket of salt, I test the Alk,Ca,Mg,pH at 1.025.
Doing this solves 2 common problems :
1) Is my test kit accurate and/or getting old....IO/Kent and many other salt mixes have their parameters published to compare to. If you do this for every bucket/box after a while you can see the variability in the salt QC and your testing....with good records this makes a measured salt mix a good standard for comparing test kits etc.
2) Find out about a bad bucket of salt before killing your reef!.....find out about that mixing screw-up ....before killing your reef.....find out about that bad electrode/test kit/uncalibrated refractometer....before!
This is a standard lab practice...I didn't realize it wasn't common with reefers.......esp after the IO high alk event! We use about 4 200gal buckets per year...making the extra test costs less than $10 GOOD insurance IMHO. and I highly recomend it.
Cheers John