you can use excel, or hydrogen peroxide works great and is cheap.
the hydrogen peroxide is the only thing that kills hair or other algae in moss without killing it, excel wil kill it if you put it directly on it hydrogen per. doesnt.
get a pippette and put 3-4 ml of peroxide in it, turn off the filter and slowly slowly slowly slowly slowly squirt it on the algae, i mean slooow. it will bubble up when you know you got it. it will turn red next day and its dead.
3ml per gallon is the max hydrogen peroxide you should use