Stained wound and skin

At the GP when collecting medicine (last last Sunday evening)
Very young part-time staff who dispensed the medicine to me said: "This is for washing." ("This" btw refers to Potassium Permanganate solution of unknown concentration)
Me: "How much water should I add to it?" (I also know it's for washing, so damned obvious, but how? No instructions on the label except to wash twice a day! Btw, this is the first time I'm using such solution for washing.)
She (also don't know) went to check before coming back to tell me: "Mixed one capful of this with two capfuls of water".

At the Polyclinic during consultation (last Saturday morning)
Doc: (after some examination) "How come your wound's so dark...?"
Me: "I wash with Potassium Permanganate."
...
... the x-ray didn't show any fractures (phew!)...
... then the doc sent me for dressing...
Me: "Do I need dressing?" (I mean I haven't been applying any dressing for the past one week and now I was told I need dressing? The GP told me to leave it uncovered.)
Doc: "Need."
(I wonder why)

At the Polyclinic during dressing
Nurse: ... "为什么黑黑? 你用了什么？" (Second time... for a moment, I wonder why didn't she know there's this thing called potassium permanganate?)
Me: (repeat) "Because I wash with Potassium Permanganate."
Nurse: "Did you dilute with water?"
Me: "Yes."
Nurse: "You need to dilute until it's light pink in colour. Else your skin will be stained brown and become unsightly."
Me: "Huh? Is it?" (No wonder the doctor also asked... and is this why my knee become the centre of attraction for a few days?)...

鸡蛋糕！