They can be pretty sensitive and prone to diseases when you mix sources and introduce new stock. Other than that they are considered pretty hardy and long lasting .
They originate from water with very low PH where bacteria or other pathogens are barely present and their immune system is not eqquiped to tolerate high diversity and bacterial count present in water with higher PH . That's why most of the discus keepers tend to keep their water and environment as clean and sterile as possible and insist on Barebottom tanks with less decor and plants and large an frequent waterchanges .
Having this in mind Bulk WCs with fresh water IMO would be considered better than daily drip and mud or soil would be considered counter productive to the discus needs for fresh and sterile conditions .