Dissolving 800 lbs of magnesium sulfate in 200 gallons of water. Perhaps unsurprisingly, this takes a long time.
OK, Elephant in the room time Paul........ LOL
????????
Ohhhh, no particular reason......
I'll give you a hint: a hydrometer is involved. My wife got a flotation tank (http://www.zenfloatco.com), and I am setting it up.