Thanks! I believe this was also posted on Jake's site, but it's been a while. I overdosed iron in an experiment with Porites lobata and saw exactly what that writer expressed - the corals' tissues darkened as they apparently concentrated iron (it wasn't an increase in photopigments based on chlorophyll analyses.)Check out post 62 on this thread
https://www.reef2reef.com/threads/lets-see-your-t5-sps-tanks.135858/page-4
Todd