What causes this?

[greenpassion]

Hi all. I have to phalaenopsis orchids that continue to have the mottled look to their leaves. When I posted about this earlier it was suggested that they had a calcium or magnesium deficiency. So I went and bought some Cal Mag and have been using it weekly with every watering. Don't know if the pics show it but the older leaves are much more pronounced than the newer leaves which tells me there's been some improvement. I'm guessing the older leaves will not go back to their normal color, but I see a slight bit of it in the new leaves. This phalaenopsis is grown in straight medium to large chunk bark. It is 1 of 13 that I have in my light Garden that I have posted pics of in the past. This orchid has bulbous growing roots, and is coming out with a new Leaf again. Other than this strange discoloration of the leaves it appears to be quite healthy. I am confused at what the issue is.