I found 4 dead Tilapia so far and it was due to my own mistake. Yesterday I was cycling the water where I simultaneously siphon out the water and replacing with new tap water. I usually do a half and half where I leave half of the old tank water and add in half new tap water.
Yesterday I forgot to switch off the tap and it ran the whole night. This morning the tank was crystal clear and the Tilapias started showing signs of distress.
I hope some do survive, tho 2 of the bigger ones has died since this morning.