algae

I set up a 92 gallon corner tank in late march 2005. I used the fluval
filters which the previous owner had used, and my tank cycled quickly and
smoothly, in fact, I don' know if it cycled at all, anytime I ever tested
the water everything was well within the optimum parameters. Anyway, after a
few weeks I started getting brown slime algae on the glass and rocks, and
then I added two clownfish and a sailfin tang, along with my four damsels.
Now, two months later, I am noticing this new kind of algae, it is a stringy
cobweb looking strands of aqua- or blue-green colored, and it is basically
on the substrate only. The substrate is those little white particles, I
think either crushed coral or crushed seashells. I notice my sailfin tang is
always sporting a round, well fed looking belly, even first thing in the
morning, when he hasn't been fed by any person for at least ten hours. I
have read that this fish is an algae eater, but I have yet to see him
working on any algae or algae bearing surface. Bu I have noticed the tank
glass is easier to keep clear, I haven't cleaned it at all for over two
weeks and it is just barely starting to get a little algae on it now. Is
the sailfin tang or some of the other fishes eating the algae? if so, why
can't I observe them doing it. I will add, when the tank only contained the
four damselfishes, they spent much time hiding, and they were timid. When I
added the tang and clowns into the aquarium, all of a sudden it was and is a
three ring circus in there, with fish chasing each other and swimming all
about the place, begging for food, digging holes, etcetera.. The man in the
fish store predicted that, by the way. I meant to ask, is anyone familiar
with what type of algae I have, and does anyone have any opinions on why my
tang looks so well fed all the time when I haven't fed him or seen him eat?
Also, any opinions on whether it would be inadvisable to add a small trigger
fish to this tank? Also, one other thing, when I added the clowns and the
tang, I also added two 'turbo' snails (sounds like an oxymoron to me) and
one of the snails died in eight hours, and the other died after eight days.
Anyone have any ideas of what is going on in this tank? It looks like
everything is okay, but I figured I'd ask. Mike.