Chalk (Calcium Carbonate) question

given my very soft water I've determined I need to add this to my mash for a Dry Stout I'm brewing. The nearest HBS is about 45 min away and I don't want to pay shipping on a $4 item. I was going to buy calcium carbonate powder from a health food store, I can't think of any problems with this, given it doesn't have other ingredients, but wanted to check with the accumulated mass of knowledge here first. Any issue with this?

Product is NOW Foods - Calcium Carbonate - 12 oz.

Thanks.

Looks fine to me...