From the experts at Soil.Ninja:
 
We hold our hands together in prayer for no crispy edges or warped leaves, Calathea (Goeppertia) and Maranta are beloved staples of the indoor horticulture industry and for good reason, their colours and striking foliage are truly one of a kind.
 
Using a blend of: Coco Coir, Perlite, Vermiculite, Fine Pumice, Activated Charcoal, Worm Castings
 
Prayer plants have a very interesting structure And definitely run top of the list for the thirstiest plants that we keep. Though we do recommend only watering we have rainwater or filtered water we always include activated charcoal to help combat the chemicals in our tap water that may lead to the common problems we all face, whether this is crispy edges irregular or deformed growth or even terminal rot, this mix helps protect against that the addition of vermiculite means it stays relatively moist long after being watered keeping those fine, sensitive and thirsty roots happy and healthy.
 
Meanwhile, activated charcoal, pumice, and perlite increase aeration and detoxify the substrate. Have other plants that have a tendency to be terminally thirsty? Perhaps a Fittonia or Aphelandra? Feel free to use this mix with them as well!