One thing that you have to know is his tank is brackish. Brandon is trying to pull a fast one on us
I'm thinking that there is a chance that the drift wood in the tank could be releasing tannins, but that usually leaves the water brownish. The rock could have something coming off of it, but I doubt that it would last this long. It looked like you had used an aragonite sand, what is the pH of your tank? Do you know your other water parameters?
Good to see you around the boards, by the way.