Hi Drew, By algae, think you mean those two hair balls of green stuff on the wood.
First, think you must test for phosphates in excess of 0.5ppm with a PO4 test kit. But, the test kit only tests for inorganic phosphates. (See the other post "A Very Odd Question"), but you may have read my response to it already.
Now, I don't really know what type of algae you have, but think you can safely assume phosphate levels are at least partly to blame.
Here is what I would do right away. Add a pouch of API Phos-Zorb to your filter. Take out the carbon if you must to fit the pouch in the filter, if it's an HOB type. In a few days the phosphates should start going down. You could also add an airstone or power head to get your water moving more so there are no dead spots or areas of low filtration.
I do hope others with more knowledge of algal types will ID the stuff for you. It does look like "hair algae" thou. But, just remember one thing, algae is algae and they're all caused by essentially the same things, too much light, too much phosphate, too much feeding fish food, tap water with phosphates, etc. You do NEED to test your tap water thou BEFORE doing any water changes, especially massive WC's!
From the photos, it does look like you have a real nice set up!