I use the refractometer in my lab to do checks and I've also calibrated my swing arm hydrometer against the lab refractometer (repeatability is excellent) for doing quick check ups. The lab refractometer is calibrated daily.
I did a copper test earlier in the week with my HPLC. Aside from a little signal noise, it was undetectable. I actually use the HPLC for an elemental analysis to save on having a bunch of test kits. Waaaaay cheaper. Well, way cheaper when you have free unlimited access to a $100K HPLC
My new sand bed is a mix of new sand (actually old sand that was dried out and rinsed like no tomorrow) and a few scoops of sand from the old tank to help seed it. I can say with almost certainly that there is no excess of anaerobic activity. I have other critters that are far more sensitive to H2S and they are happy as clams (er... sorry for the pun).
Magnesium sulphate is used as a muscle relaxant for snails to anesthetize them before dissection, I don't know if it has the same effect on brittle stars though. I don't think this is the cause though because my strawberry top snail was acting funny before this.