Railer, this is going back some years, but I had a similar situation with harlequin rasboras that I purchased at petsmart. They were on special at $1/ea and I had a tank that had been running for some time with just shrimp and snails. I bought a dozen of them. They were tiny, but lively, good color, bright eyes and would eat like crazy. Within something like 10 days, one by one, they all died.
Unrelated, but given your fishless cycle is complete, you might wanna start new threads with your unrelated issues. Things are going to get lost and mixed up if you keep adding to this one.