Is this BGA or something else?

The stuff is very dark little globs which "hang" (up) on the plants - +boyancy.
Slimy, very smelly. Globs appear black, but are really dark green. Stuff
"pearls". Stuff will float off if plants are brushed. The water gets cloudy. A
prefilter (just floss) on the filter intake will turn a blue green, and
eventually to deep blue toward black. It gravitates to the above gravel line
"roots" (whatever you call the nutrient collecting tendrils that grow above the
gravel line) and fine leaved plants like firl or water sprite. Tends to mostly
show up on the edge of broader leaves. In the evening this will cause the
appearance that the plant is pearling, but I think its the ??? algae/bacteria
that's "pearling".

I tried maracyn, but at the 1/2 dosage recommended on the rec.aquaria notes on
BGA. It did diminish during treatment (but I was running a diatom filter at
the same time) but has now returned. If this is just BGA, do I now go back to
maracyn but at the full "sick fish" dosage? (when I can get some more
maracyn).

Many thanks in advance,
Sharon