Ok so I have been taking care of my friends fish for about a week and it died. I haven't fed it or anything but fish find their own food so that can't be it. I was thinking that it's because I didn't clean out that tank but she did that the day before she left and said she does it every two weeks. Then I thought maybe it's just an old fish but she said she hadn't had it that long. I can't tell her I killed her fish can someone help please!