Better to make yourself a colloidal silver generator out of 3 9 volt batteries a couple of wires and alligator clips and a pint fruit jar. Well a d one ounze silver bar cut in half. Now you have a strong antibiotic. The instructions for assembly are on the internet. We have one and make our own. That and 70% oil of oregano will get you through most illness that requires anti biotics.
In my experience 21 volts is WAY too much voltage to run my colloidal silver generator.
I use about 12v.