G'day Kellin,
You have a bit of a mystery going on there by the looks. Your WC schedule is good, as are your numbers...and your choice of foods...are the discus the only inhabitants?
Prior to introducing the discus to your 72gal, did it house other fish? Did you do a fishless cycle or use mature media from another tank? Have you noticed any stringy white poop at any time?
Since you are not seeing slime coat issues my guess would be something internal, like Hex. I am far from an expert, but I have fry from the same pair as you. I successfully treated them for Hex with pure metro 500mg/10 for 10 days after moving them from the their previous owner to my tank. Sometimes fish carry pathogens and are resistant to them until a season of stress, then the pathogen can create sickness.
I am sure someone with more experience here will chime in with an answer, or more questions to move towards and answer, but in the meantime I would add salt at 3-5 tbsp/10gal. I have recently had a great experience using double that dose for a mystery sickness during the hero fish strategy. It is stressful at that concentration so I am not recommending it for your juvies, but in smaller doses has a soothing effect and may hinder the multiplication of whatever pathogen you're experiencing.