One day my dad decides hes going to do a 100% water change because winter is here. I come home to find him changing 10k gallons worth of water with low 30 degree F water right out the hose when its snowing with no water conditioner. Had about 80 fish koi/goldfish and two carp die. The shock did kill off a decent amount but he added about two bottles of highly concentrated copper based algae killer thinking it was water conditioner which killed most of the reaming stock. Never thought someone could be so clueless continuing to shock/burn/kill the fish after telling him what hes doing is wrong, my dad is Hitler of the fish species.