I have a 10.5 gal bayou classic kettle. It was purchased used as part of an electric set up. I'm not sure if the previous owner passivated the kettle. My issue is what appears to be beer scale build up. It takes a lot of time to clean but I have not been able to 100% remove. I'm thinking passivating might help prevent the build up. Directions on the web show 4-10% solution. I am having a hard time trying to figure out how much citric acid to use for 10 gal if water. I've read numerous posts but I cannot figure out how much to use. Can someone help to determine the amount?