I had the same thing happen to me today in one of my tanks!
I have around 60 small Garra Rufa fish (Doctor fish) in each of 2 independant 90L tanks.
2 died yesterday and 2 today in one of the tanks. all that was left of them were the bones! they were completely stripped, no sign of any flesh...
That's what i did! I had the filters running for a couple of weeks before the tank was delivered.
Not sure if its the best idea tho. The nitrate levels are high 8 weeks later! How often do you do water changes? and what percentage of water do you remove and replace?
Martyn