aluminum hydroxide as an electrolyte
When you are applying 31.9V across I am assuming cm-ish distances, you are definitely causing a lot of electrochemistry to happen in the solution. 

You are oxidizing one of your aluminum electrodes to $\ce {Al^3+}$, therefore precipitating $\ce{Al(OH)_3}$ and probably reducing water on the other electrode to evolve $\ce{H_2}$.Along with these, you are probably doing a lot of other reactions with any and every impurity around, but these two should dominate.

Measuring ionic conductivity properly requires doing an AC measurement since you cannot have a sustained DC current without doing electrochemistry of some sort. The electrochemistry on the electrode surface ends up the main factor influencing your measurement in any DC setup.