11-18-2009, 07:24 PM
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What Angel means by "liquid concrete" is very hard water, the last thing you want for plants or soft water fish. Calcareous rock (limestone, marble, lava, dolomite, coral) slowly "dissolves" adding calcium to the water and raising the hardness (which is basically calcium and magnesium) and pH as well. The vinegar test usually works, though some argue that vinegar is not a strong enough acid (after all, we do drink/eat it on food). The acid which I think is in regent #2 of the nitrate test kit is better, a stronger one. if it fizzes at all, don't use it.
The other thing is rock can absorb all sorts of toxins like pesticides, oils, anything it may have come into contact with. It is always a risk.