Better yet, go to your local pharmacy and pick up a carton of Epsom Salt (Mg) for less than $2.
If you dose a mineral mix (traces) the odds are that you probably don't need to dose extra Calcium.
I definately need calcium, all my plants got the squiggles, lost my last snail three days ago, and some of the leaves on my moneywort have white spots. Also, my gh is EXTREMELY low.
Get some dolomite and either mix it into your substrate or add to your filter. You can get a 50lb bag of it at just about any garden supply store for under $10.