Wow, I'm really sorry about your fish.

How are you treating the ich?
If temps are raised, is the aeration increased also?
When you say the dead fish didn't have any marks, do you mean other than ich?
Could be they were really weakened by your ammonia spike (it was extremely high) and
Ich. It can be in the gills and effect their ability to breathe.
It's just so unusual to have a massive loss of fish like that. Did you add dechlorinator with your last
water change? Any soap residue or lotions on your hands or arms?
Any sprays used in the room that could have gotten into the tank?
Again, I'm so sorry, that's a rough deal.