Mr. Lee it is so good to see you again.
Are you growing them indoors or outdoors?
If indoors that could be the problem. To much moisture, not enough light and not enough air circulation.
If outdoors you are probably giving them to much moisture and maybe not positioned for enough sun?
Can you show us a close up photo?
I will definitely post photos of my project when I get started. Cliff is making me a frame to hold the rock wool substrate so it can hang on a wall or fence. Meanwhile
I will use a plastic nursery flat for the form to hold it all in place.