Joe, I've been using my e-system for over a year now, and believe you can not leave a skillet in too long. My observation is that sound metal is not affected by electrolysis when using similar metals. I'm using a stainless steel anode. For dissimilar metals, you'd probably get ion transfer resulting in plating. As long as I have current flowing, I get the bubbling - think that is the result of current going through the electrolyte, not the cast iron "cooking". Finally, I've had times when I ended up CAREFULLY using the tip of a drywall spatula and occasionally, a regular screw driver to remove persistent carbon that just won't come off. I always put it back in the e-tank afterwards and then use 0000 steel wool, which removes any trace of tiny scratches from the spatula/screw driver. Good luck!