http://animal-world.com/encyclo/fresh/i ... seases.htm
a great site for any and all diseases you may encounter with remedies
I never ever purchase live stock from loval stores, I only purchase from Dr Fosters & Smith LIve Aquaria or That Pet Place, the shipping overnight is high, $35.00, but I have yet to ever have a dead fish. When I purchased from Petco, Petsmart around town, always wound up with dead fish. The shipping is worth the cost. You always get healthy fish from the places I quoted.
White spots mean the fsh store has dirty tanks from either over-crowding, over feeding, not enough water changes, just poor conditions. It is called ich. The site gives you a full descrition of this problem.
Sorry to hear about your loss; I never like any loss, but it's only nature just ike you and I will someday die too. We just must take precautions for things of this nature to not occur or cut down on the them occuring.
I hope the web sites and pet stores online help. Take care