Cyanobacteria Treatment

I posted a couple of weeks ago about a problem with algae in my
aquarium. (Search for "Algae ruining hobby for me" in
rec.aquaria.freshwater.misc). After posting a picture, respondents
identified it not as algae, but as cyanobacteria.

Upon the advise of the posters and the Internet community, I procured
some erythromycin and began treatment. I scrubbed everything in the
tank as best I could and did a water change. I've since been treating
with 1.2 grams of erythromycin every day for the last 4 days (it's a
55 gallon tank).

It doesn't appear that the cyanobacteria is spreading anymore, but
that could just be wishful thinking effecting my perception.

How can I tell if the cyanobacteria is dying? Will it change color,
or just disappear or what? How much longer would you recommend
erythromycin treatment? I don't want to make any resistant strains of
cyanobacteria and release them into the ecosystem when I do my next
water change.