Thing is they eat a lot, poop a lot. Stuff builds up in the substrate producing nitrate and breeding bacteria in higher concentrations (Discus are sensitive to bacteria in general) and it leads to a better chance of stunting or sickening your fish
Polyaddict86 hope you don't mind but here's a photo of my mates setup, or a bit of it:
Polyaddict86 hope you don't mind but here's a photo of my mates setup, or a bit of it: