phosphorus and nitrogen deficiency

Imo, I'd use a little citric acid/ascorbic acid/tartaric acid and perhaps some sugars. The citric acid can aid nutrient uptake (particularly phosphorus), ascorbic acid (vitamin c) is also beneficial, tartaric acid is essentially a potassium source and sugars are well..sugars. Lemon, lime, other sort of acidic fruit juices could be used too. I probably wouldn't use vinegar much (maybe balsamic vinegar or apple cider vinegar).