Unless your keeping wild discus or angels there's no need for soft water.
I'm pretty sure some people around here are even keeping wilds in plain tap water after they get settled in.
I've kept domestic discus in 400 tds water with no problems.
The only time you might need soft water for domestic discus is if your having bad hatch rates with a pair and want to drop the tds.
You'll get this same answer from most people around here.
Have fun.