Ok customer did say they were yellowing before he sprayed a product called wilt-pruf. I believe him.
My final diagnosis is chlorosis from too much water. He was watering every week with 2-4 5 gallon buckets each.
I would imagine the clay subsoil was not letting the water drain.
So what should I do in that case next time I hit overly hard clay?
1. Raise the ball up and add soil
2. drill drainage holes into the bowl (although it is all clay anyway)
3. Backfill with all clay to remove void space for water to sit.
Could I remedy this by adding a clay cap so to speak above the roots to lessen infiltration of water?
What do you guys do?