Horror stories! Man I've got well, ummmmm, NONE. Thats because I quarantine everything. Thats kinda the point I guess. I have however avoided flat worms, red bugs, zoo eating nudibranchs, ich and possibly a plethora of other shizen that never did make it into my display tank. Grim, no offence taken man, just don't want to see another thread that starts like this.
"Hmmm, I put a new fish in my display tank and now all of my fish have these white dots on them?"
Or like this.
"I've had it with this hobby, I can't seem to keep my fish alive."
Come to the dark side Grim. Set up that quarantine tank.
