How much water is needed per tray for iontophoresis (Dermadry) ?

Hi,I’ve just received my Dermadry iontophoresis machine and I had my first session today.I was wondering: how much water do you pour in each tray? I tried not to put more than 500 ml per tray like the manual said but I don’t know it the amount of water I pour is enough,can someone give me a precise amount per each tray (like 200/300 ml,idk). Furthermore,I had a max of 3 mA today,how do you think I should manage the voltage for the next sessions?