RIP Rory2 and little cory

Well, he was staying on the bottom and he developed a white patch on his face. I medicated the tank and found him dead this morning,along with one of the young corydoras.

Poor fish, I am sorry if I did something wrong, I still don't know what it might have been.

But now there are only a few platties and two corydoras. Cories need each other's company, even three was too few. Five or 6 would be better.  But if there is some disease in the tank, maybe even in the fish themselves, there's no point adding more only to infect them. I don't know how many I have lost, can only see a couple. I have a very bad feeling about this.

Guess the answer is a total water change, in case it is a fungus or some bacteria that might kill the lot. God, I want to give up this tank.