Brassia (Bratonia) yellowing leaves on new growth

[Oranagra]

Hi,
My Bratonia who in the past couple of years produced nice growth is not looking so good lately.
The leaves on the new growth started yellowing.

The only recent changes i can think of is that i moved it to semi-hidro about half a year ago, and that 3 months ago i started adding gypsum to my rain water since this forum helped me realize my Catts are suffering from Calcium deficiency.

I don't think these are the reasons, so maybe someone has a different theory?

thanks.