I'm sorry to hear about the little guy. It's hard to tell what happens sometimes.
Time for update, all 8 are going well and growing. Wow do they eat like crazy. It's insane. At least 5 cubes of fdbw or more per day along with pellets on a timer (not many) and frozen food too. Here is a video, I think they are looking good, great color for their size and they seem to have a good eye/body ratio from what I can tell. The light isn't the best and hard to feed one handed. One got scared and hid, but don't worry they all eat like pigs. I have been doing at least 100% daily changes, with the amount they eat I don't see how you could grow a large batch and not change that much. Of course I don't think they have to be fed this much!
https://youtu.be/4IEkEjWKPeE