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Really, the best advice I can give someone buying from the above mentioned retailers is just to try to buy them when they are on sale and buy 2-3 x's as many as you really want because its likely if you do that you MAY end up with the actual amount you want that are healthy after two weeks.

I agree completely. And would like to add that these fish must be put in a quarantine tank (QT) for at least 2 weeks so the sick fish won't infect all the fish in your main tank. Only after you have not had any illnesses, oddities, growths, or deaths for 2 weeks in the QT would I consider it safe to add the fish to the main tank.