The 'new' snails also could have come in on the plants that
you put in. And been reproducing.
I'm not sure Japanese trapdoor snails are all that prolific.
I've added them numerous times to my ponds and have never seen them reproduce.
But stranger things have happened...

I would watch the tadpole population. If you find that the pond seems to get
overwhelmed by them you can plan for next year to remove some of the spawn when
you see it and transfer to natural body of water. You can also do that with
some of the tadpoles in the earlier stages when they are easier to catch.

Are you planning to add fish to this pond? They will take care of much of the
snails and tadpoles. Doesn't sound like you'd need to feed them at all. With
this size of pond (15'x45'x3' to 4'
deep) and keeping your stocking level low you'd be okay without a filter as it
sounds like you have a nice assortment of plants.






kathy :-)
algae primer
http://hometown.aol.com/ka30p/myhomepage/garden.html