Fish Still In Quarantine

A few weeks ago I bought 6 ember tetra to add to the 5 I already had. When I got them home, one had a dodgy looking lump on its side, almost like an air bubble. I have a shrimp tank so popped it in there for the time being, fully expecting it to die, or something to happen.
It's still there, and nothing has changed. Still has weird lump on its side.
What should I do now?

There's been no change whatsoever?

I'd be inclined to wait another week (four in total) and if there's been no change by then, put it in with the other embers.