First off, don't panic. If you do, you will end up taking a minor algae problem and turning it into a disaster. What you have is something that looks ugly, but is not a disaster as far as crashing the tank goes.
Also, your tank is rather new, so it's more likely that this is just a phase it's through. Whatever you do, don't medicate the tank to try to control an algal problem. Those products work, but unless you correct the underlying problems, all you'll do is replace one problem algae with another.
You'll also notice that a lot of people with this problem were dosing something or other. I can't prove there is a link, but I'm very suspicious about it. I think you did the right thing by stopping it.
What sort of clean up crew do you have in the tank? You may want to increase that quite a bit. Some people take this to the point where they have 1 snail and 1 hermit crab per gallon of water. I don't think you need go that far, but if I had this issue I'd use a mix of snails and hermits. I'd add about a dozen of each and see how you do. If you find you need more you can add them.