Why is my Calathea latifolia not healthy?
Your plant might need a little more humidity, or you could be more consistent with your watering schedule. I think the best thing you can do is use soil that drains well so that the soil stays nice and moist.
Have you ever thought about trying a mixture of planting media like compost, pine bark, coco coir, worm castings, and perlite? It might be just the thing for your garden!