I have a horrible problem with my soft water (at least for african people, SA Cichlids love it) I have never been able to keep a single snail in my water from tap. It comes out around 6.5 with no GH or KH that I can read on my test kits, and I have tried several. What I have done was add lace rock, or even crushed coral wrapped up in a porous material, like panty hose. Its Calcium based and works great. It does dissolve slow, so its probably best used in smaller tanks (I have one in my 20 gal shrimp and snail tank and it works like a charm) but I have a large piece in my 125 in its sump and now my snails dont dissolve anymore! BTW anything Calcium based should work.