Don't worry, it takes most people a bit of time to get the hang of a new forum!
I'm wondering the same. The fact is slimy makes me wonder if it's a biofilm type thing, especially since it's fairly easily removed. I'd stop all the excess chemicals and just work on manually removing it, and trimming back any 'dusty' leaves even if it means cutting back quite hard, and see how things are looking in a few weeks after some maintenance and some large water changes. Seems a shame to cut back such large beautiful java ferns, but they're already impressively sized and green, I'm sure they'll bounce back quickly enough! I also think it's sometimes easier to manage a potential algae outbreak if you're overzealous about removing it before it really gets a good hold.
Wait, what are you using in your filter? Any kind of balls or pillows or anything like that?