The female guppy we got on Sunday was dead when I came home at around 7. I'm really sad but I want to know what killed her. She was pretty active the whole 2 days we had her, but would not eat. Also this morning her scales seemed darker than the day before, but she was acting normally, so I ignored it. What do you think killed her (maybe her time at the pet store?), and should we take out our other fish as a precaution (it's a 10g)?