I read many growers in the tropics like Indonesia use plant vitamin B1 to help orchids in such condition. For organic fertilizer, many recommend rice water, onion/ garlic peels, fish/ meat water, etc. Caution: this might have a strong odour. I do not give my plants vitamin B1 though, because I cannot find it where I live. I do not water my vandas with those organic fertilizers either because I grow them indoor. Good luck!