Just lye, but when I decided to go with lye, there was a transition where I added lye to the sodium carbonate solution I was using at the time. When I moved, the solution was replaced with lye only.
You can mix them however you want. The important factors for an electrolyte in our application is that it is a "strong" electrolyte (it ionizes completely, because the ions allow the current to flow) and that it raises the pH of the water. I have been using lye because it makes the pH higher - a lot higher - than sodium carbonate. My experience is that my anode requires less maintenance and lasts longer with NaOH than with NaCO3.
You should determine how much lye to use on an experimental basis. If you like to hit a No. 5 skillet with 40 amps, you will need a more conductive solution. I rarely have more than 20 amps flowing, even on a No.12 skillet. My opinion is that 10 to 15 amps is adequate for what I am trying to accomplish and the extra current is a waste of electricity that doesn't get my iron any cleaner than 10 amps. If your system is a 55 gallon drum, you will need more than it you are using a 10 gallon Rubbermaid tote.
I would get your system set up with clean water, put in a large pan and your electrode, and turn on the charger. If your charger has an ammeter, that will help. Pour in some liquid caustic soda (like one of the drain openers that is a lye solution), thoroughly mix it with the water, and see what current you get. Do this a few times and you will be set. I'd also start by adding a pint per 20 gallons - start slowly until you see how the system behaves. Remember, you can also adjust the flow of current by separating the pan from the anode.
Jeff
