Is your calathea going limp? Try cultivating them in water. Keeping houseplants in hydroculture is a bit unconventional, but easy to care for.
Calatheas are picky when it comes to watering, so this is also the most important aspect of care. If they don't get enough, the leaves quickly form dry spots; if they are kept too moist, they are prone to root rot and are easily attacked by pests such as fungus gnats. You should always add a few drops of hydroponic fertilizer to the glass of water.