Hi Squid
When I refer to the pandas as being delicate, I mean that they just don't seem to have the sturdy constitution that most of the other corys have. Where others can fight off a disease long enough for the medicine to work, pandas seem to give up right away.
I don't know why they are this way, but it might have something to do with the conditions they are raised in (farmed or tank raised commercially) or perhaps too much stress for them during long distance shipping. It could also be that they have trouble adjusting to different water conditions and have lowered immune systems as a result. Or, it could be a little bit of all those things. I have noticed, however, that ever since I have been keeping pandas that were spawned and raised in my tanks, they are much stronger and healthier than the ones I originally bought.
Prevention of problems seems to be the key to success. Rapid treatment, at the first sign of distress is absolutely necessary. While I don't usually recommend treatment of fish until you are sure of the diagnosis, I make an exception in this case. Early treatment is essential.
I've seen seemingly healthy pandas look fine at night and the next morning woke up to a few dead ones and the rest covered in spots. MelaFix is mild, but seems to help greatly. If this happens and you don't see results in the next day or two, it's doubtful they will survive long enough to undergo a course of treatment with antibiotics or other medicine.
It's funny how sand seems to stick to corys. I've had many a scare over this.
) But still, if you're in any doubt, put in a dose of the MelaFix. In this case, it's better to be safe than sorry.
That might be something to be concerned about where the pandas are concerned. 
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The risk is not worth it. I'd use water changes and carbon in the filter to remove it first.
