The AF may be supplying the trace elements needed by the corals to color up. I have been testing a new trace element dosing system and I have found that the corals need the proper amount of trace elements to really take off. When I started this new trace element system it was quite shocking to see the growth of corals really. As before this I was seeing some growth but once the corals got the proper amount of elements in the water it was eye opening for me. Having been in the hobby since the early 80's and having tried every "method" out there this was the first that showed me positive movement in coral growth. One learns something new all the time in the hobby.