My 1.5 year old clowns have parasites. Fear of loss of another fish.

[PhishFriends]

I've had these two clowns in this tank for roughly a year and a half, and something has just changed.
I added a frag about 3 months ago otherwise it's been a year or so since I've added any fish of shrimp in
Last weekend the only other fish, a starry blenny died. No external signs of illness, eating and being his mischievous self. Next morning I found him dead.
I've since noticed these stringy poops from my black photon clown. They seem to be the thickness of a thick hair and are clear/white. My other clown seems healthy.
Externally not signs of ick, no heavy breathing, still eating excitedly. Stringy poop after every meal.
What is my best course of action? I don't have a qt setup currently, but could do so quickly.
I've never treated for parasites before.

 

[PhishFriends]

I want to add to this, 80 - 90% of the time I feed frozen brine shrimp. Pellets are mostly when I'm away for a day and setup the auto feeder.
I'm not seeing any obvious behavior issue, but want to catch it before anything gets bad.

 

[Sharkbait19]

Brine and mysis shrimp can cause white, stringy poop like that, so I wouldn’t immediately jump to parasites. Have you noticed any change in behavior from the clowns?

 

[Lavey29]

Need better pics of the fish under white lights