I was planning to get a school of cardinal tetras. I called petsmart and they had 4 of them for about 5 bucks each. I then called the LFS and they said that they didn't carry them because they were so hard to keep alive and that they were really only for advanced fish keepers. They did offer to order them for me if I wanted them though for about the same price as petsmart. What gives? Is this species really that sensitive?