I would try out crushed coral and see if buffering it helps raise your pH to an acceptable level. Its probably one of the more consistent ways of buffering your water. You could also try baking soda, but that would have to be added at every water change. I have no used aragonite, but anything that will increase the hardness will help. You want your goal to be 7.5 minimum for the snails and the cherry's will do fine in that range as well.