Is it slimy? It almost looks like cyano, but I don't believe it comes in green... How often do you feed? What is your lighting schedule? What kind of filtration do you use? How much flow is in the tank/how many powerheads?
I'd say that lack of slow is one of the issues you are having, though not the cause of this. You have shown us almost all of your tank and I don't see one powerhead.