Ebjd help he's sick

Treat with Metro and Epsom salt soaked foods. depending on how big the tank is I'd treat the whole tank with Metro as well and definitely use it for a dip bath for the fish since he is not eating, and definitely dose the entire tank with Epsom salts. White feces is a sign of hexamita, use metro and if it isn't to far gone he should pull out of it. Also what are your water parameters? ammonia, nitrite, nitrates, ph if you can, all that.

Epsom salts or regular NaCl? you need Epsom salts, not aquarium salts. I recommend quarantining the ebjd and treating him separately, and vacuuming and changing the water in the 125. treat the main tank too, if it is hex its contagious and more than likely spread throughout your main tank already. Get the sick fish on metro asap as well. Also, get your nitrites down. Have any pics of the sick fish?

I'd suggest finding a 5-10 gal tank, or at the very least a bucket or Rubbermaid tub and get him out of the main tank. You need metro first and foremost though, so I would focus on that.