My first betta set I lost one
I bought 2 Veiltail betta females and the next day I noticed the one wasn't acting like I have seen most fish doing. So I called the pet store and the manager told me to just watch her and if she gets worse to bring her in so I went to bed and woke up the next day and she was nose first in the water and not moving. I was so upset that my first fish I ever owned died but I think that she was on the verge anyway of dying and the shock of the move just finished her off.
America (f, HM), Spirit (m, DBLT), Rescue (f, VT), Missile (m, HM), Purnurple (m, HMPK), Dragon (m, VT), platies, mollies, sorority tank of 21 females, AND lots of guppies.