Gray coloured moss sounds like Black Brush/Beard Algae. It's from inconsistant CO2, more simply put usually from lights being too strong or on too long for the amount of CO2 that is in your water. Overdosing Flourish Excel is the best way to get rid of it, but there's other ways too. Look under The plants/ferts section of this forum to find a sticky on how to deal with it.
As for Coral, I'm not sure.
As for Coral, I'm not sure.
