Besides misjudging fish's temperment which i'm sure everyone has done, there has been a few (not all by me, but by my little sister as well)
1)she decided to wash my dad's salt water collection, WITH SHAMPOO
2) she decided to give his cichlids a makeover, with makeup and mascara
3) i was young and put fish into scortching hot water, without even attempting to acclimate them at all. (That's how i killed my favorite fish
4) I was selling all my cichlids (they had gotten too big) and took all the rocks and shells out that i had made their caves with, and went to the store, sold them for store credit, and came back to set the water up for a new batch of their offspring, as i was setting the rocks up, i pick up a shell and one of my neolamprogous daffodil fish fell out
dead obviously
1)she decided to wash my dad's salt water collection, WITH SHAMPOO
2) she decided to give his cichlids a makeover, with makeup and mascara
3) i was young and put fish into scortching hot water, without even attempting to acclimate them at all. (That's how i killed my favorite fish

4) I was selling all my cichlids (they had gotten too big) and took all the rocks and shells out that i had made their caves with, and went to the store, sold them for store credit, and came back to set the water up for a new batch of their offspring, as i was setting the rocks up, i pick up a shell and one of my neolamprogous daffodil fish fell out
