leaves sunburn

[4NICK]

why each of my flowering orchids definitely leaves yellowing.........

[kiwiorchids]

What kind of light conditions do they recieve? i dont think it is sunburn, possible a deficiency in a particular mineral, perhaps N2 (nitrogen)or K (potassium)? I would mix 2-3 grains of Potash with about 3 litres of water and water your orchids with yellow leaves, and if that doesnt work after about 4 waterings (once a fortnight), try with a nitrogen soluble fertilizer at half strength.