Softened water vs. well water

I am about to build a small pond (a couple hundred gallons) and am wondering
about what water to use. I live in the country in central Texas (aka the
Hill Country) and the water that comes out of our well is very hard, with
plenty of calcium compounds, some iron and some hydrogen sulfide.

My plan is to initially fill it up with water straight from the well (I
figure it's good enough for native fresh water fish that live in our springs
and creeks). We have long hot summers here, though, and I know I will have
to be replenishing often due to evaporation.

This presents two problems. One is concentration of minerals from
evaporation. I figure the solution is just to pump out some old water
regularly. The second is the constant refilling. I wanted to install a
trickle supply from the tap (the well is too far away to run pipes to the
pond). The tap water has gone through a water softener, though, that tends
to leave a lot of sodium chloride in it . So eventually, through refilling,
the pond will mostly contain somehwat salty tap water.

Am I going to have problems growing fish in this water? Are there certain
species that will do better? Would potassium chloride be better than sodium
chloride ?
Any info appreciated. Thanks,
Sam