As for dealing with it.
I recommend removing what you can with your hand and a siphon. Pick it and suck it up with the siphon with your other hand, you can use an air line tube so it doesn't empty your tank too fast. You don't want this stuff floating around in your water column.
Reduce the time your lights are on to 6 hours a day until it starts to get better.
We'll help you try to figure out why it's growing in your tank.