I'd never heard of the vinegar test before! I may well be adding new, more natural rocks to my tank!Isabella said:Your tank looks beautiful - the driftwood and plants make it look very natural. I love tanks that look natural. I also got my stones from a river. But before you use any stones/rocks that you collect outside, make sure they're safe to add to a freshwater tank. Pour a few drops of vinegar on them and if they fizzle ("bubble") they can't be added to a freshwater tank.