So.....
I called the lfs yesterday morning. I know the manager very well and we are on good terms.
Discussed the situation with all the options. And he recons that there is either a parasite (requiring a dewormer) or a flagellate issue (requiring Metro). I don't have qt facilities, so he offered me to bring it in:
And either leave it with him to treat
or to swap for another one.
I watched him feeding the ones in his tank
Decided on balance that I would prefer to swap.
So that's what I did.
Hopefully this second one will settle in quicker!