As for crawling out of the aquarium, how sealed does the cover have
to be?---I have just a standard hagen plastic canopy (modified for more
lights) with cutouts for the filter and heater etc. We don't want to find
snails in our kitchen cupboards eating all our cornflakes or anything.

LOL! That's not likely. If they get out, you're likely to find them crawling
on the floor, likely along a baseboard. They won't get far, being snails.

It doesn't have to be sealed that tight. Just tight enough so that the adult
snail (which is about the size of a brussel sprout) can't easily get out. The
one time I had one escape, I had too big a gap around the filter tubing. It
had crawled up the tubing, right out of the tank. I made the gap smaller, and
haven't had a problem since. (IME, juvenile snails don't try to climb out. I
think it's the females looking for someplace to lay their eggs that climb out.
They need to lay their eggs above the waterline -- which, in a fishtank, is
often on the underside of the hood.)

Btw, how fast do they clean up hair/thread algae? The stuff that I had on
the driftwood and a few java ferns is slowly spreading to the new plants.
Can it get too much or too late for pomacea to clean it off?

IME, no. The kind of algae that grows in the glass, and black brush algae get
tough and unpalatable when they get old. But hair/thread algae seems to remain
tasty no matter how old it is.

However, you can't depend on algae-eating creatures for perfect algae control.
An algae problem in a sign that something is out of balance in your tank. You
should try to fix that, in addition to making use of algae-eaters.


Leigh

http://www.fortunecity.com/lavender/halloween/881/