Osmosis water without hardening for vampire crabs in the terrarium?

Hello everyone, I urgently need your help with my terrarium. I have a 60x45x60 Exo Terra with lots of plants, ferns, moss, and I keep Red Devil Vampire Crabs. For some time now, the water in the terrarium has been very calcareous, which is damaging my plants, especially the moss. The plant leaves turn whitish…