Your post would have fit nicely in the Container Gardening
section, but it works fine in this section, too.
I think you should gently run a dull knife, something like a dinner knife, around the root ball of your plant and slide it out of the container so you can look at the condition of the roots. Doing this won't do any harm to the plant as long as you're gentle with it. It will allow you to see whether the soil in the bottom half of the container is very wet, or if it's dry.
The reason to do this is because underwatering and overwatering both result in the exact same symptoms on the top growth of the plant, i.e. the yellowing/browning of the leaves, usually beginning with the lower leaves.
At the same time, you can check on whether the plant is root bound and needs to be moved to a larger container. If all looks well, then make note of whether your plant needs more or less water, whether there is a problem with the drainage, etc. If there is some root rot present, you can use a sharp knife to remove the mushy roots, too. If you need to repot the plant, be sure to use a soil designed specifically for container-grown plants. No other soil will work correctly within the confines of a container.
Your plant is one of the few that doesn't want to dry partially between waterings. It wants to be kept evenly moist. My Calathea is the same way. I touch the soil each day as I walk by the plant, and if it feels at all dry (usually it feels cool to the touch if it's wet enough), I water it and let all the excess water drain away. Never
let it stand in water in it's drainage saucer.
One other thing that can cause the leaves to yellow and brown like those on your plant is too low a temperature. Being placed too close to the breeze from an air conditioner could do it. They want temperatures above 60Ã‚Âº F. They also dislike sunlight, so must be kept in bright indirect light at all times. I would allow one to receive an hour or two of very
early morning sunlight, such as between dawn and 10 a.m., or very late evening sunlight, such as just before sunset.
That's about all I can think of to say about Chinese Evergreens right now. If you have any more questions, feel free to ask.
"Isn't it enough to see that a garden is beautiful without having to believe that there are fairies at the bottom of it too?" - Douglas Adams