Bad news folks: the results are in and the vet has a very high certainty that it's mycobacterium (TB). We're going to send the samples off for the histopathology to make sure and get a more detailed analysis what exactly is going on (specifically if there are any parasitical or other bacterial infections that would be more treatable), which should take 1-3 weeks to get back.
So far, he's not recommending nuking the tank, at least not yet. We're doing research and working on some strategy ideas, but I don't have time to go into them at the moment (we're about to start boarding).
I have a lot more information to share, including pictures from the microscope (with explanations!), info about the disease, and more about the gameplan now. Unfortunately, I didn't have time to post all that info before work and it'll be a pretty late night (and busy few days ahead), but I'm going to do my best to get that posted within the next 48 hours or so.
Thanks again everyone! Stay tuned for that more-detailed update...