A few months ago I started using Brewtan B (high MW tannic acid) in my mash and sparge water. This followed a brief experiment with low dissolved oxygen brewing. Although I ditched the LODO process I decided to retain Brewtan B as it binds copper and iron which are catalysts for oxidation reactions. I also started adding salts to my sparge water. One day I noticed my sparge water had turned a rusty brown colour and after further inspection realised my urn element was breaking down. I had been experiencing some muted hop and malt flavour in my beer so decided to ditch the urn for a new Birko with a concealed element. So today I brewed and added brew tan B and gypsum to the sparge water in the urn. A few hours later and I notice that the urn water has turned green. A quick search and other have had a similar experience. I'll brew tomorrow and ditch the Brewwtan, but curious as to what is going on?