Ive had horrible luck with columbian sharks,..I can never seem to switch them over to marine, something happens in the middle of the process, or I wait to long.
baby peacock bass.... or maybe they are already sick when i bought them.... by far the biggest lost money wise 320 bucks! the toughest has to be plecos , i had 1 bristlenose burried under 5cm of gravel with no water for about 20 mins ( i didn't realize that i scooped him up when i took all the gravels into a bucket)
my noen tetras don't seem to be able to die theyre so hardy its like they are zombie tetras
for me pictus cats always die and so do goldfish ive baught like 20 in the past few months and i now have only 2 thay are sposed to be the easyiest fish i can keep one of the hardes discus but not goldfish