Green Beard Algae
All I've ever dealt with is the hard dark green stuff that's generally sponge-able. I left my tank for a measly three days and now I can barely see in it (exxageration)
How do I get rid of this?
(Additional; cories in the tank, so if you recommend a chemical it has to be fish (duh) AND cory safe.)
A severe lack of trichogaster.
Just because your Gourami is sick does not mean it is always Iridovirus, DGIV, Gourami Disease, et cetera.
Look at all the other factors in your tank before coming to this conclusion.