Alex,
When I make 320 I start electrolysis at about 30 degrees C. Then I allow it to steadily rise getting to between 75 - 80 degrees ONLY BY THE END OF THE RUN!.
I make 1 litre batches always so i'm in for about 5 hrs. 20 minutes at 15ma.
The expansion as it starts to heat sees volume increase beyond the 1 litre mark and I have full coverage of the 1 litre beaker with a lid (breather hole in the centre only.)
I have NEVER ended up with less than 1 litre by the end! try gentle increasing of heat rather than wacking the cell straight in at high temp. It really doesn't need it. As long you are above the solubility limit and you're reducing and electrolyte is accurate you should sail through the batch.
It never tastes metallic.
I do filter but in truth, if you are diligent and careful with anode / cathode cleaning during the run, you shouldn't get any residue.
As Kephra says, any drinkable water AFTER production is fine. I put it in tea, coffee, orange juice, distilled water, filtered water..........
Well done on the run!