They actually like warmer water, but if you get the pH below 6 they struggle and definitely don't thrive like discus. Reasonable hardness doesn't bother them at all. There are a lot of people that have decided they can't be kept that way, but I've not only kept them, I successfully breed them in harder water. The fry seem to be hardier in harder water, also. I know a few people that no longer modify their water with them and are totally happy with the results. Modifying it to get them to start spawning is definitely recommended, but after that, they aren't as picky as they get credit for, just because they're expensive. The batches of fry are small, so it keeps the price up is all.
Barbie