If it is not burnt due to the hot intense sun there , then I will say it is fertilizer or salt burn.

When was the last time that you flushed your mix with fresh rain water or bottle water of all the accumulated salts from your fertilizer and or faucet water?
When was the last time you repotted into a fresh mix?
Is your mix very porous?

I hope this helps

Mike

Thegidget. Calatheas, especially Roseo Picta types, 'like yours,' are difficult, especially in dry climates.

An east window is bright enough to keep your Calathea healthy, yet, not too sunny to burn leaves.

I live in the midwest where air is very dry during winter. Calatheas are a job and a half over-wintering.

One thing you can try is placing your plant on a saucer w/pebbles and water. Water should not touch the pots bottom.

Continue misting.

Every so often soak pot in a sink/tub/container so water is sucked through drainage holes until soil is saturated.

Don't keep soil soaking wet. It needs to dry between waterings, (moreso during winter months.)

Calatheas are slow-growing, therefore do not need constant fertilizing.
Once a month, during growing season is adequate.
My Calatheas are fertilized with Fish Emulsion. FE has a little fishy odor, but it's natural and will not cause root burn.

One other thing you can try is, saving water. I keep cleaned milk containers filled w/water. When Cals need a drink, the water is room temp and chlorine free.
Chlorine effects plants in different ways. Some plants are sensitive to Chlorine and cause leaf tips to burn, so give it a try.

Good luck, Toni

Hi Mike.

I can't help but I thought I might chime in with my experience. Mine went from the bedroom to the kitchen and in the kitchen it grew fine and healthy as well as in my bedroom. Then I placed it in the bathroom and the leaf tips are starting to brown although not as bad as OP. I don't know how to explain it; I thought it would love the extra humidity in the bathroom but I guess not. Perhaps the constant sway in extreme hummidity from hot showers to very low is stressing it out.

I have a C. concinna by the way.

Hi Musa. When your Calathea was in the bathroom, was it getting fresh air or was the room stuffy?

A lot of humidity w/o circulating air can cause problems.
Rot, especially if soil is constantly wet
Fungus gnats.
Too warm. Cal's don't like it hot. Leaves curl and brown when over-heated.

Since your Cal preferred the kitchen, perhaps you should leave it there?

During warm days, leaving a window ajar helps

Can someone help me! What is the best prefer potting soil you can buy for the Calathea plant . I hope some one could give me a good advice on a soil. P. S thanks