I water once or twice a week (tubwater 230µS), as fertilizer they get Orchid Quick(up to 600µS), unfortunately I dont have the exact composition, sorry, but I never cared as I use it for 8 years without any problems. Would you recomend Epsom salt?
urbanianum might be a little too light, but in general I'm satisfied with the leaves of my Paphs. What I'm most concerned is the William Trelease, the second leaf (left side on the Photo) has yellow stripes which look extremley unhealthy to me. btw all plants get the same treatment.
I agree with Ray. Try magnesium for a few fertilizing sessions. Epsom salt at 1 teaspoon per litre works for me. A little kelp helps for more root formation. Watch roots carefully not too salt them too much.