I have had this calathea for 9 months, it did pretty well through the winter to my surprise, it's always had some brown tips and edges, I know they are rarely perfect and often drama queens.
However, over the last couple months I have noticed the browning, yellowing & crinkling getting much worse, as you will see from the pictures, so much so that I am losing quite a few leaves and I struggle to find an unaffected leaf.
I haven't changed how I care for it (at least not to my knowledge)
It is in a medium to bright spot 1m from a west facing window
It is still in its original nursery pot inside the cache pot.
Over the winter I watered it roughly once a week, at the moment it has been hot so it is more like twice a week at least, it is very quick to wilt when it is thirsty, the soil is still usually slightly moist when this happens.
I water with rainwater. I have a humidifier in the room & also mist the plant every morning.
I have leaving the window open to help air flow & benefit from the outdoor warmth and humidity at the moment.
The house is also never goes below 18 degrees.
If anyone has any ideas it would be greatly appreciated. As it never dries out i'm concerned it could be the roots, or maybe fungal?