How many days do i water the Calathea White Fusion?

The short answer is that whenever they need water, you should water them. Calathea needs moist but well-drained so don't let it dry out or otherwise don't overwater so the leaves won't turn yellow. Let the top of soil dry out before giving water. The soil moisture level is important for Calathea.

I think it would be great if you could water it once every nine days.

This plant usually doesn't need much attention, but it's always nice to give it a little water every now and then. I find it helpful to do a finger test by inserting my finger about an inch into the soil. If it feels dry, it means it's time to water! You can even make it a habit of doing this once a week or once every two weeks.

I usually water it once a week during the summer, which is excellent! During the winter, I water it once every 2-3 weeks, which is perfect! Here's a great way to check the soil: just put your hand a few inches into it and see how it feels!