I just got in some ember tetras but they are slowly dying on me. I bought 6 for my 10 gal then 2 died 3 days later. Then another died the next week. I'm really disappointed because I waited 8 weeks for these guys to become available. Anyway they looked fine then one turned pale, refused to eat, then died. This is slowly happening one by one. Water parameters are good, temp is good and I can't think of any reason why it's happening. Are embers very sensitive to water softness or anything like that or is it some disease?