you only have to use the 99.999 silver IF YOUR GOING TO DRINK IT.
for herming a plant, you CAN use sterling ( in a pinch) BUT silver coinage is best and cheapest . get yourself a couple of cheap silver quarters. there 97 percent silver and work great. they tell you to use pure silver and not sterling or jewelry silver if your going to drink it because sterling and jewelry silver ( including us coinage) has nickel and copper in it, which is poisonous to ingest.
also, make your CS up as you need it as it only takes a few minutes, dont have it sitting around cause accidents can happen such as spraying a plant with CS when you only wanted to mist it with regular water. ive made CS right in the spray bottle.
