From the description the algae is some form of brush algae. This is the only algae I have issues with. Light and nutrients being slghtly out of balance will trigger it. Jaysee's suggestion of tube age is pertinent, I have had this algae increase from old tubes, but they should last 12 months or so.
I used to have this increase every summer, until I worked out that the cause was the increased length and intensity of daylight entering the room. Two ways to deal with this. Block the daylight (simple blinds may not be sufficient, I had to use these plus lined drapes), or reduce the tank light to compensate.
Do whichever until the algae is no longer increasing. What is there will not go away, just leave it. As new leaves emerge and are algae-free, the older leaves with algae can be removed. Usually they will begin to yellow and die from this algae, though not always.
I would not expect a nutrient factor, if things have been good for a year or more, unless you have adjusted the fertilizer somehow. I had this algae suddenly cover all the swords in one tank, and dealt with it by cutting back the fertilizer from twice to once weekly. Things can be different from tank to tank (I have 7 running), it is a matter of finding the balance that works and then if algae incrteases determining what has changed.