Heckels tend to be very timid and easily spooked by movement and noise. Green and Blue/Brown discus not so much.
Try and keep wilds in as close parameters to their natural homes as possible - different species of wilds have different requirements. It is possible to keep wilds in non-ideal conditions. 3dees has done it, and I used to as well. However, you will notice a difference in behaviour and comfort level of the fish when you start to emulate their natural conditions.
I kept Heckels in tap for over 2 years with no issues. They were healthy and happy and beautiful. However, when I switched to RO water and started emulating their natural blackwater habitat, I could see a huge difference in their comfort levels. Suddenly, the perpetually skittish discus were extremely bold, and their colours started to pop even more than before. Try it - you will like it (and so will your fish!). If you are not comfortable with using an RO filter, then keep Blue/Brown discus. Their natural water conditions are very close to most tap water (pH ~7ish and TDS can be above 100-150) so you can see them at their best without the cost/hassle of a RO filter!