Overnight growth of algae- help!?

I have a ten gallon tank- with 5 guppies. My snail of 6 month just died a few days ago ;( and when I got home tonight EVERY plastic plant, ornament , piece of gravel etc was covered with a 2 millimeter layer of what looked like animal fur or what I'm guessing is some type of algae. I have always had some green algae on the walls, but this is hairy and black. My tank is not in direct sunlight- I feed them a pinch of food every other day, and change 25% of the water every 30 days. The tank has been set up for about 8 months w/ no problems. I freaked out when I saw what took over and took out all of the plants and did a 25% water change. What is growing and how do I manage it? I leave the light on from about 7:30 am until 8:30 at night-so 13 hours...but it has never been a problem. I keep the temperature at about 80 degrees...