Calatheas dying

[Edyth63]

Hello, my calatheas were doing just fine for a couple months and then they started to shrivel up and get brown edges. I noticed they were dying and decided to make a new substrate. One part sand/miracle grow soil/orchid bark/ and sphagnum moss. They seems to be doing okay but now it has gotten worse. My room stays between 68-75 degrees. I have an AC but they are not near it. My humidity stays around 55-65. I used to use a humidifier but I would get high 80's so I stopped using it. My room usually stays at a 60 % humidity without doing anything. I do not use tap water. I'm not sure if I'm under watering or over. I have a moisture meter and it usually lets me know it's getting dry so I water them but even when I do they look the same. Any help would be appreciated