welcome to GoY
I would use a greneral slow release fertiliser like osmacote granules.
as for the discolouration that could be due to being damp flowers or the whole plant getting too dry. sounds like i am hedging my bets but drought and drowning have similar symptoms.

is your pot large enough? it is a climbing plant that grows quite tall, you could try top dressing by removing some of the soil at the top of the pot and replacing it with fresh and feed it then. as its on a balcony does it get a lot of sun that dries it out too quickly, and have you used the right compost, and do you keep it moist all the time, i know how difficult it is to water right to the roots in a big pot ( some people use a short pipe pushed into the soil so that some water will reach the roots --sorry for all the questions but they are just a few ideas for you to consider hope it helps...