Well here is a snippet from the University of Google....
"Most of the time it is not a good idea to water your garden with softened water. The reason for this is that softened water typically has a high amount of sodium, which is gotten from salt. Most plants cannot tolerate high amounts of salt. The sodium in softened water actually interferes with the water balance in the plants and can kill plants by âÂÂfoolingâ them into thinking they have taken up more water than they have. Softened water essentially causes the plants in your garden to die of thirst."
And here is what I use sometimes to Fertilize my orchids.
Peters Excel Calmag Finisher
13: 05:20:7 Cao:2 MgO+ TE 1gr/litre.
So How much Calcium is too much.
Hopefully someone who really knows this stuff will answer your question.

This post was edited by arthurm on Sat, Nov 22, 14 at 3:02

When I moved earlier this year, I had to consider installing a water softener. I researched using KCl as an alternative to NaCl. I found several sites and articles supporting the use of KCl as an alternative to NaCl because the waste water could be used for irrigation in gardening and lawn care. My understanding was that water softened with KCl was safe for most house plants also. I did not find out anything specific to orchids. Ultimately, we did not go with a water softener so I don't have personal experience to share. I am attaching a link that may be more helpful than I.

Here is a link that might be useful: Alternatives to Sodium