I've found that healthy well conditioned discus will spawn in most any water. Getting the eggs to hatch and raising the fry can be daunting.
IME if the TDS is over 150ppm you have no shot. Ideally I look for it to be just under 100 and that might mean mixing RO water with your tap. Very often one or both of the parents will eat the eggs or fry. It may take a few spawns for them to stop this behavoir. I've had to remove a few notorious egg eaters (but only one parent at a time).
I use 29g tanks for the breeders, change water at least once a day, and keep a supply of live black worms in the tank at all times. It's imperative to wipe the glass clean with each pwc, and rinse the sponge filters in tank water daily as well.
A drop in temperature from 85F to 81F will stimulate spawning. Good Luck.