Erik - any chance of posting a picture? I have red hair algae right now, but my tank is going through its swamp phase (just cycled and has very high nutrients), and it is located on my rocks. It looks exactly like hair algae except it is red. How old is your system?
Another thing you can do is test for the presence of phosphates. Take a water sample from the water column, then take a sample about 1/2 inch down in the sand where the algae is growing. This will help determine if your phosphate source is from the sand bed. If you have any growing on the live rock you can also take a sample from the rocks.