Voltage goes down with the CS production progress

Dear all,

I bought a voltage/current control board available at ebay:

www DOT ebay DOT com/itm/181340066014

The board has good construction and it is easy to set.

Today I used it for the first time to produce colloidal silver using a 24 volts 500 mA as power source (board input).

I set the board to output to 24 volts and 5 mA. The things go well in the beginning, but according the CS production progress, the voltage goes down and down. Removing the rods from the distilled water the output voltage goes back to 24 volts; reintroducing, the voltage goes down again. The higher is the CS concentration, lower is the output voltage, going lower than 9 volts.

If I set the current to a higer value (eg.: 10 mA), the voltage reacts and rise.
At this moment, with the current is set to 13 mA, the voltage is around 10.3 volts.

If I set the current to 70 mA, the voltage goes to 24 volts.

Maybe the voltage/current control board is not suitable for this kind of use, droping the voltage as it "sense" a kind of short-circuit resulting of the silver in the distilled water.

Did you guys had similar problems using other solutions for control current?