SICK discus help!

[Rayvan]

One of my discus hasnt been eating for 3 days and been hiding in a corner and today i saw her poop clear white. can someone tell me what's wrong with her plz and how do i treat her
i did a 60% water change and tested my water par
PH 6.5
KH 4
NO 0
temp 29c
i have has her for 4 months and she's usually the one bullying all the other discus but now she's just hiding can someone tell me what's wrong with her.

 

[Lupin]

Looks like she is riddled with internal parasites. Unfortunately, discus are very prone to this issue. What do you normally feed her? Mammalian protein often makes them prone to internal parasites as the meat serves as their breeding ground. To battle this issue, administer praziquantel which you can buy as Prazipro and metronidazole (available as Flagyl in pharmacies). Prazi can be dosed at 2.5mg per liter. It does not come cheap so be aware of that and prepare to shell out a bit more cash. I'd treat all discus with it if I were you. Use Flagyl by a tablet of 250mg per 10 gallons. Afterwards, arrange an annual deworming by using a combination of prazi and metro, flubendazole or fenbendazole.