Hi,
Thanks for your replies, here's a photo of the first leaf that went brown with some other more recently browned leaves next to it.
The growing conditions I'm not too sure how to describe... temperature-wise the area it's in goes from ~32-15 degrees in summer-winter, water-wise I used to water it 3 times a week, then it seemed to be getting too wet (and the temperature dropped recently so it needed less water) so I reduced it to about once a week. Medium is a mix of long fibre sphagnum, cocopeat (rinsed, no salt), and perlite.
If there's anything more specific you'd like to know please mention it!