Hi Sylvia,
I don’t think, that there is any sort of snail, that is able to cope with that soft and acidic water. All the snails (the most common ones like: http://en.wikipedia.org/wiki/Planorbarius_corneus etc.), that came into my tanks along with the plants, became more transparent and smaller from one generation to another. Finally, there weren’t any left. Of course, they need lime for their shells which is completely absent, and not stable, in our tanks.
Last week I’ve visited a friend, who is using Asellus aquaticus in the tanks for raising the fry. They don’t seem to be a threat to the eggs and the fry, but they eat dead artemia and unfertilised eggs that would otherwise moulder.
Of course, adult Paros eat up the Asellus.
I think, this could be worth a try.
Greetings,
Martin