BUT, 30g sounds like waaay too much, GP.
As Galbrew said, you've got to check what your local water report is like (& your recipe), but given pretty much all melbourne water is between soft to very soft, i'd say it's ~5x too much.
As a comparison, i'd use 1-3g gypsum in the Mash, bit less in the sparge, bit less again in the boil (manticle's method, kinda). Plus CaCl2 & MgSO4 in various similar quantities also, depending on what i'm trying to achieve.
I'd also suggest using a little Acidulated malt, lactic acid or citric acid to get your pH down, *if* you need to adjust the pH - there's only so much the salts seem to be able to do without adding handfuls.
Back on topic, as mentioned above (mant's etc), i'd get a set of jewellery scales from eBay. I got a pair for ~$7-12 from memory 2 years ago. They measure down to 0.01g, and seem to be quite accurate (as calibrated with water volume measurements).
FWIW, the first one i received was a dud, so i got a refund, and the 2nd one i got is the one i'm still using (that's perfect).
So not totally infallible, but worth the risk of the occasional dud, i reckon.
2c