For me it would be my cory. I love her and all but when I bought her, I was told by the lfs that she'd do fine in a 10g tank but really she needs at least a 20gJoker77 said:I guess I'm talking community tanks as species only tanks you probably should know what your getting into beforehand.
For me I guess it would have to be my red eye tetras. They where almost the first fish I bought. I don't really like them because they like to hide(unlike most of my other tetras), eat alot, their rather bland looking and worst of all they annoying steal the algae pellets when I put them in (they are meant for the loaches/plecos). I can't see myself ever buying them again.