Can you hook your voltmeter to the electrodes and watch the voltage while you do your next batch? I suspect you have a Constant Voltage Generator, which means the voltage stays the same from beginning to end.
If it is a current controlled generator, then you should see the voltage decline substantially before the timer shuts off.
I suspect that you have a constant voltage generator, which is NFG. Also I have read in detail the website and everything I see suggests a constant voltage generator.
If true, you can easily fix this problem with a 1 Mah current limiting diode placed in series with the anode..
Confirmed by Ben [email@example.com], "The voltage is a constant 56 volts DC."\
This explains why you are making Silver MUD.