i'd definitely start by taking about 2/3 of that floater out and see how that does for a bit (keeping up with removal to that extent once or twice a week).
when my floaters get like that in my 30 i'll see the same thing. sometimes a little algae starts showing up around my ambulia if it's starved for light enough. i skim the top pretty good leaving a fair amount of open space and almost like magic the tank seems to repair itself.
hmmm... and i'm sorry... my last post may be a little misleading. i would add root tabs to my list of course. osmocote is only $5 for enough to last quite a while, though, so no big deal, really.