Algae's Getting Out of Hand

That type can be a real pain, almost nothing eats it. If those are plastic plants, take them gently from the tank and give them a dip in boiling water a few times. Reduce lights a little in the tank if possible, and reduce feeding a bit. This gunk needs neutrients and light to live, so reducing both will help your infestation.

I would reccomend against putting any new fish in there to eat it.

Mostly called black brush algae... I think it's some species of Audouinella. This stuff is a real pain to control. On the other hand, once it covers everything in the tank, it's sort of pretty. If you're drunk.

You could investigate Siamese algae eaters because they are about the only fish known to touch this stuff... but having tried that myself I'd say think twice about introducing a fast, active fish that grows to 4" or so and will much, much rather eat fish food. Mine didn't put a dent in the stuff.

Nutrient control seems to work if you can get it right; planted tank people usually have some good advice in this area.

I only had it when I accidentally introduced it on a plant; it's never spontaneously popped up in my aquarium and I don't think it's normally resident in my water supply. When I did a total tear-down in frustration after six months and started all over after bleaching everything, I never had it again.