Microscope on floating algae

My eleven-year-old son wants to be a chemist.  (Go figure  :-)
So, a year ago we got him a 450 power microscope to play with.

He recently showed renewed interest, and we prepared a slide
with some floating algae from my 180 gal. community tank.
(BTW, I have lots of floating plants with good floating algae
growth, which I skim every few weeks.  It seems to be a good
environment for my many small tetras and pencil fish).

Anyway, I was quite surprised at the variety of biological
activity in my tank.  I suppose I shouldn't be, because I do
have a biological background.  However, we found several 
different one-celled organisms, some very small worm-like
?nematodes (tons of these), and some (relatively) huge
eggs.  Huge compared to a one-celled organism, that is.
These are not visible (I think) with the naked eye, so they
are certainly not fish eggs.  I'm guessing snails?

Do you think these very small organisms are effective
food for anything other than the smallest fry?

So...do ramshorns scatter their eggs in surface floating plants?
I have a couple MTS snails also, but I've never seen them up
at the top of the tank.

If anyone on this list has access to a microscope, I highly
recommend looking at samples from your tank.  It's quite
impressive (excellent resolution on different types of algae!)
and has given me a much greater appreciation to the big thing
sitting in the middle of the living room.

Sorry, my microscopic biology is not all that good, or I
would try to identify more.  However, I do think twice now
about carefully washing my hands (with soap) after cleaning 
my otherwise pristine all-plant tanks.