I saw your plant pics and symptoms appear to be consistent with
overwatering however, some of the pics look like nitrogen deficiency. I
assume the white stuff in the medium is perlite which may be holding
water in the medium due to it's "draw up" effect. I guess for lack of
information that you may consider experimenting with more free draining
media and see if there is improvement. Questions arising include
microclimate (full sun, 80% shade, hot house etc), watering reginme.
ambient climate, location. The thing I am surest is that it does not
appear to be a fungal attack on the leaves. Hope that helps.