A simple tip for you Fred, clean your plates with vinegar (strong solution) then hock up your plates with +nnnn- meaning four neutral plates
Then go buy some distilled water or "battery refill" water, go to you loqal hardware store and buy a box of pure LYE (NAoH read the label, pellets most likely and with NO aluminum in it)
Start with two or three tea spoons of NAoH/LYE first in 4L of distilled water, this way you can control how much your cell is going to draw/how many amps, the more LYE the more amps (conductivity of water)
You would like to have less than 2V pr plate gap and at 12V and 4 neutrals you should be in that range
This way you keep your plates clean and no "gunk" in the water
Good luck and happy testing
Mr H2inICE