i have a 40g tank and i started with 8 damsels which were (2 blue damsels, 2 green chromis, 1 yellow tail, 1 domino and 2 yellow damsels) within 3 days my domino died. i dont know why either. then a week after i added 4 blue damsels and 2 dominos. ive read and heard that dominos are really...