Wally wrote in message . ..
Take a look after the lights have been out for 3 or 4 hours, your jaw
will drop. I went through a thunder storm power outage here in Dallas
last night and was checking the fish about 3 AM and there were many
thousands in my 110.

I have probably several hundred in my 50, but I don't see them unless
I really look for them, they take care of leftovers and dead fish, and
also eat a bit of algae. To boot they drive any other snails which get
into the aquarium extinct (by eating their eggs).
Personally I consider them beneficial.
I avoid them in breeding tanks, though, as they'll also eat fish eggs.