it doesn't look like Ammania or Alternanthera to me. Alternanthera is dark red or purple emersed, and the stems when above water are covered in knobby seed things. Still need better photos of the stems and leaves.
Could be Hygrophila corymbosa species, or Gymnocoronis spilanthoides. If you got it at a store in the USA, it is more likely to be something common. Both these plants are common in the USA pet trade.
Hygrophila corymbosa "cherry leaf", or H. stricta, Nomaphila stricta, "Giant Hygro" or "Green Temple" are all the same plant. The leaves can get a pinkish color sometimes under bright light and in young leaves.