Their behavior was calm, they explored the tank from time to time. They all liked to stand on one of the rocks, and they spent a lot of time there. Although the death of all was the same, they were swimming normally, and suddenly they collapsed with their belly up and sometimes turned on their axis, until they died. I'm sorry I did not give these corydoras the conditions they needed, so I will improve the system before purchasing new corys.I'm sorry to hear that ! How did they behave the day before, and just before they died?