A little over a month ago I lost a bunch of african cichlids that I had growing out in a plastic rubbermaid bin and all of them died except one which was a cynotilapoia axelrodi. It was a huge mistake by me, I had them growing out in the bin for about 2-3 months and about a week prior to most dying I did too large of a water change (there was no gravel in the bin btw and doing the large w/c killed off all the beneficial bacteria I assume) and it wiped them all out except the cyno. axelrodi.
I'm not sure if thats what you meant by hardy...