The effects of prolonged carbon use on marine fish have recently been well documented, but the same cannot be said for corals, particularly SPS corals according to Leng Sy of EcoSystem Aquarium. Recently Leng added 2 liters of high-grade German carbon to his experimental 550 gallon, SPS-dominated reef aquarium. In short time, he began to see bleaching on many of his SPS corals shown below. Leng believes this was due to the removal of essential trace elements by the activated carbon he introduced. He has since removed the carbon and completed a 250 gallon water change and has reported that the corals are beginning to rebound. What do you think of Leng's theory?

I didn't find the right solution from the internet.