Most drinks have synthetic minerals and vitamins. Carbonated water is not good for your stomach.
For Psoriasis two things you need to do is eat raw organic plant based diet, no processed foods at all, eggs are ok, and do Liver Flushes multiple times every three weeks.
Most people fast and then go back to what they were eating, processed foods, high animal protein and GMO- fake foods.
I hope you get to your goal of 15-16 days, it is doable. Sometimes it is better to do short fasts than a long fast. This is what I do, fast every now and then two-three days. Right now I am on my 8th day, but hoping to break it tmrw.