Well after putting the loam I am using into my tank as a cap I began to wonder what all was in it. First step the vinegar test. I threw in several of the larger pieces and to my relief no bubbles. I then threw in some of the very fine grain pieces (sand like) and a few of them bubbled (I would say maybe one or two grains out over every heaping tablespoon) Not the best thing but at that amount I am not reeeallly worried. Now the weird thing happened when I crushed some of the larger stones. Almost all of them nothing happened but then one started to bubble (not a lot but enough to notice). Why would a rock not bubble whole but then when crushed react? Either way it is to late now as I will not be tearing down my tank to deal with this issue, I guess I will deal with what might happen whenever it does happen. It a good feeling knowing that I will have issues with my tank before I even have a single plant and or creature in it.