It's possible that the LFS had a pH of lower than 7.0 ppm. This would mean that the fish would have a hard time adjusting to the pH in your tank, especially if they weren't acclimated gradually. Your pH is slightly high, but it is best not to adjust it. If it's possible, ask your lfs what the pH is in their glassfish tanks.
Did any of the other fish in your tank die, or are any acting abnormally?
Was the tank cycled, or was it in the process of cycling?
Do you know the ammonia levels in your tank?
How much time passed from when you released the fish into your tank until they actually died? How many glassfish did you get, and did they all die? What was their appearance like before they died? It could be that they had a disease or illness before you got them, and happened to die once you put them in your tank