I have been researching killifish and am interested in adding some to my 29 gallon. I have looked at several websites and some they can tolerate very hard water while others say 4 gh is the cut off. My gh is 10-12 so my water is decently hard, but not extremely. Would killifish work in this hardness? Is there any reasons why they aren't a popular fish in the hobby? Neither of my LFS or big chain stores carry them.