I use 1 tablespoon per gallon. Almost always get a white film on the first one or 2 pieces, but seems to go away. I always thought it was non-disolved soda. My amp guage never reads more than 4 or 5 amps, and have never had a reason to add more soda to try and get the amps to read 20. My feeling is if it's bubbling, it's working. I also get the green slime if I leave it in. My water is hard, and rusty. After a dozen or so pieces, the water turns green, so I discard and start over.