Sadly both of the M. picta died in quarantine over the last two days.
Visually healthy, active, eating, behaving like hoplo cats do - I woke up one morning and one was gone, the other the following evening. I returned to the store and found that the entire shipment of them kicked the bucket and the tank they had been in is now quarantined.
The lesson: If you can wait to buy a fish from the LFS
, give it a week or two there before you do so. I was a bit overzealous since I had been unable to find them before, and now I'm out $40 and have contaminated some of my other fish with (presumably) what they had.