Discus Parasite Help

Hi, I am asking on behalf of a worried friend/Discus owner. They have noticed a worm like parasite on one of the dorsal fins see picture. Any advice welcomed?

Thanks in advance.

Hello
Thes pests are caused by infected pores on the fish. Usually they are a sign that you aren't doing enough water changes. If you are lucky they will go away if you do a few daily water changes. They will return if you dont keep yourwater clean enough, being a minimum of 30% weekly.
What are parameters pH GH KH NH3 NO2 NO3 ?

Need a clear picture of the white thing where it is attached to the fish/ fin.

It could be excess mucous, clear stringy white fish poop, or an anchorworm. However, anchorworm are very uncommon on discus.

What does the fish's poop look like?

Try waving some water over the white bit and see if it washes off.