White poop on established coral beauty

[The Coug]

New reefer here. I’m the relatively new owner of an established tank. It’s got 4 fish, a coral beauty, one spot foxface, cardinal, and blue tang. They’ve all been in the tank a year plus. There have only been a few inverts and coral added the past 3 months.
The past day the coral beauty has had a white stringy poop. From my reading it sounds like intentional parasites.

Questions:
Do fish parasites just sprung up like this?

Should I treat? I have General Cure and Focus. I won’t be able to catch the coral beauty, she’s very shy so I’ll have to feed medicated food to all the fish.

If I don’t treat, us it likely the other fish will develop problems?

I’ve got two clowns in a observation quarantine tank I was going to add next week. Should I hold off adding them?

Any guidance is appreciated.

 

[Big G]

White and stringy poop gets our attention. But we also look to see if the fish is eating like crazy but its stomach is shrunken or pinched in too.

 

[Flippers4pups]

Does the CB look thin? Fish sometimes can carry internals for long periods of time before they become a major problem.

 

[The Coug]

No, seems thick and chunky like the other fish. It eats less than the others because it’s so shy, but eating habits haven’t changed in the past 60 days.

 

[Flippers4pups]

Okay, tell us what you have been feeding. Flake, mysis. ..etc

 

[The Coug]

I’ve been feeding a cube of frozen Mysis alternating with Rods food every other day. I also put in a quarter sheet of nori daily.

 

[The Coug]

I was able to get a picture tonight but you can’t really see the streamer well.