Yellowing Leaves

[WhiteRabbit]

I'd look at the roots - only way to get an idea what's happening there. If they have been over-watered, roots will be squishy and rotted. If under-watered, dried out. With the media you have used, I think over-watering would be hard to do at this time of year, especially with fresh bark - but, could be

I'd use a skewer in the media to check for moisture in the media.