Well, I have tons of it on my 10g too, so don't feel bad. you can
get a sponge and warm water and scrub, or, you can do like i did and get a product called
Aquarium Pharmaceuticals Safe & Easy Aquarium Cleaner. It works great. I strongly reccomend you getting it. So easy to use, and doesn't harm your fish.
When I had the tank set up I had it half full so I could breed pearl gouramies in it and when some of the water evaporated it left a white line half way down the tank.