Update:
*sigh* I'm down to a single Bolivian; 2 more died between last nite and today. I'm at a complete loss to explain what happened. Initially I thought it was the columnaris (that I'm sure of) that was killing them, but after treating the tank with Furan 2, then feeding them Pepso food as a back up after the Furan was out of the water, I lost 2 more. Neither of them showed signs of columnaris so my guess it was something else that was the cause of their demise, but I haven't the vaguest idea what. No ammonia, a small amount of nitrites but salt was added, 30ppm nitrates. I doubt it was the tap water, as I did water changes on all the tanks (and the angels laid eggs right after!) with no problems elsewhere. No signs of parasites, no obvious signs of specific disease (other then keeling over after starting to look weak and hanging out near the top of the tank, but even then their fins have been full and not clamped).
The remaining Bolivian looks healthy atm; active, feeding, good color. I did notice it chasing the other 2 around yesterday. Don't know whether the aggression played a part in their deaths, or they were getting weak then and it was taking advantange...
Anyway, learned my lesson. NO more impulse buys; not worth it in the end.
And I've no idea what to do now. Nuke the tank? The last guy looks fine; and I've no where to put him atm that won't endanger my other guys if he is a carrier of something. Plus, how to bleach sand with laterite in it? I may just move him into the 8g QT tank when the loaches are out in 2 weeks, and leave the 25g fallow for a few weeks....