I have 4 discus, average 12 cms diameter in a 240l tank, well planted. I have a colony of red cherries thriving in the tank.
Luckily, the discus are not snacking any of the cherries, I can even see some shrimps swimming freely between the discus. No fear so far! I'm lucjy with these ones. I remember 2 years ago a "young" discus I introduced in the tank and which taste a dead shrimp. H e might have found it delicious as he then started hunting all shrimps he can see.
He has been banned immediately.
As for the ones I ahve at the moment, I introduced the shrimps at night, all lights off, and everything is pefect: lots of red cherries, 4 nice discus, red noses, cardinalis, otto, nerites and 4 crabs in the tank ^^ ... but infestation if ramshorn

though, it seems the crabs are wipping a bit the ramshorns...