Depending on the quantity needed you can buy RO
or Distilled by the Gallon (.65 Cents US per gallon around my area) and play around with the mix RO
/Tap Water until you get the softness you desire.
Whattaya got and where are you trying to get?
1-55 Gal-4 Colomesus asellus, 2 C. shufeldtii
2-10 Gal-20 M. dayanum, Planorbarius corneus
1-6 Gal-4 Clea helena, 125 Red Neocaridina heteropoda
5 Gal-28 Halocaridina Rubra, 4 Neritina reclivata