Hi all, Great forum, lot's of knowledgeble info floating around. It has helped me a great deal in my homeowner maintenance quests. Well, today I drained the tank to replace the gas control valve. While I had the tank drained, I decided to replace the anode rod. Of course, I shut off the natural gas, water supply, and electric before I got started. After draining the water tank, I removed the anode rod. All that was left was a bare wire. Glad I decided to check it. After removing the gas valve, which also threads into the tank for the thermistor, I noticed quite a bit of greenish sludge in the tank. It had the consistency of whipped cream, light and flluffy. There appears to be quite a lot of it in the tank. It even was all over the thermistor probe. What's is this stuff and how do I remove it?