I am from India from the easy coast.
It is tropics. mostly humid throughout the year except in winters.
here the predominant media is charcoal chips.
Here the regional plant research center uses it.
well after repotting the plants I found few of the leaves have started turning yellow.These are old leaves.though the new ones are lush green. Any reason for this?
Are these on all of the plants or just some of them?
Sometimes, the older leaves will turn yellow as part of the natural aging process. Sometimes it's related to the roots being "unhappy" after transplanting or from damage in the prior potting media. If the newer leaves look good, you should be fine.