I second the diagnosis! Try all the usual cures and of that doesn't work, I'd recommend using one of the chemical treatments in about half the recommended dose. I did that about 1 1/2 months ago and also quit feeding frozen brine shrimp and haven't had a trace of it since.
I am planning on using Chemi - Clean. I just wanted to make sure that it was the algae I thought it was before cleaning my tank. Any views on how that stuff works?