I noticed that there is a very fine coating on the 2000w HWD elements I got from home depot. I used to scrub them with a green scrubbie after each batch. One day, I saw copper...next brew was a Rye IPA...elements scorched and couldnt be cleaned-beer was fine. Next elements I installed were still 2000w HWD, but I only clean them with a plastic bristled brush now. I also mounted the new elements rotated 90 degrees from how they are in this pic which makes them much easier to clean. Mounted like this, I had no idea what was on the bottom after a brew.