The water changes have ceased to perk up the ill Clown Loach now, he's always got clamped fins and is shimmying a lot. Definitely signs of fin rot, no doubt about that at all now (obviously before the signs were either too difficult to notice/too early stage, or they weren't actually there - probably weren't there). I've put some carbon into the filter (middle pad, the replaceable one, not one of the two main pads) for the next 36 hours or so and done a water change to remove the levacide (it had ~24 hours to do something, and I'm averse to mixing medications), will be using eSHa 2000 on Tuesday after swapping to a standard polyester pad (I know not to use the carbon when medicating). Not sure if I should try levacide again, camallanus worms seem unlikely (wished I'd never dosed with it now, I could have gone right to the eSHa 2000).
I didn't expect re-homing just yet, was quietly hoping something worked out a little later on. I appreciate what you've done for me in this situation, and I have no issue re-homing with someone else.