yeah the vinegar test is for carbonate based sand, should foam. I would stay away from lowes/home depot sand, they might have other additives that may leach into your tank. Usually that sand is not rinsed real well, and can contain some pollutants. Play sand, for a sandbox, is a better choice than the quickcrete stuff, although the most common is silicate based. Calcium based sand helps to keep/buffer calcium levels , silica sand does nothing. some say that silica sand can cause an outbreak of diatoms, but this has been a controversial issue..... i would recommend buying some sand from a fellow maastard, post in the wanted section...