While I don't recommend using salt softened water, this is what I've been using for the past 5 years since I've returned to the hobby. I live in a cold region and do wc at over 50%, so I have to mix in hot water(which is softened).
So, after 5 years if this, I'm not seeing any obvious issues. I'm running 4 tanks at the moment, raising a wide varieties of fish from different parts of the world, nearly all my fish are grow-outs, I've had plenty of breedings, and I rarely have sickness. I have a fishkeeping friend in town that also uses whole house salt soften water, and he owns an even greater variety of fish than me and is more interested in the breeding aspect of the hobby......and he is extremely successful, and not experiencing any issues with this softened water either.
Here are a few examples of my grow-outs and the varieties I keep:
View attachment 1233890 View attachment 1233891 View attachment 1233892 View attachment 1233894 View attachment 1233895 View attachment 1233896
View attachment 1233893