I'd like to offer the following suggestion regarding the setup. A 100 K potentiometer would probably cost about the same as a constant current device and would allow you to have whatever current you end up being happy with after a few experiments. If you also use a 1K ohm resistor in series, you can use your multimeter on the 2 V range, measuring across the 1K resistor and read from 0 to 2000 µA. You will find that running your set up at the lowest current and taking the longest period of time will allow you to make clear Colloidal Silver . This will give you ions, the smallest particles.
Another item that you will find useful is a quality laser pointer. Nothing from China. High-quality laser pointers have a current regulating circuit which ensures that the output of the laser remains the same no matter what the condition of the batteries. The rated power is maintained until there is no laser action whatsoever, at which time the batteries have to be replaced. The cheap ones from China will vary in power, therefore making a very poor test instrument. The laser pointer will enable you to see the generation of the small particles, as they are being made. This will occur after you have achieved the highest possible ionic portion, the ions are combining to form larger particles. In the days before we had laser pointers to use, we did not know whether or not we had made Colloidal Silver until a yellow hue appeared. The yellow hue was caused by the presence of particles larger than of 40 nm in size. It creates a yellow because the particles block the blue part of the spectrum. If you subtract blue from the rest of the spectrum, you have a red green that you see as yellow. The smaller particles are more desirable as they have more surface area.