Thanks for the tip. I didn't know tea reacts to pH.
The setup is working now with a diluted iodine solution. After I add sodium thiosulfate it reacts and the solution goes clear. Your suggestion is a bit less poisonous though.
Peter
To symbolically demonstrate the neutralization of a waste water stream I want to have a transparent vessel of water change from brown to clear after adding a clear liquid. I have found some indicators that will go from yellow to clear that I will use in a pinch (p-nitrophenol) but I would prefer...
