Remove the eggs and hand pick any snail that you see.
Your pond is rather large though!

Snail killing chemical treatments will harm other living critters in
the
pond.

You can make a snail trap, fill a bucket with lettuce and algae wafers,
suspend in the pond in the evening, by morning, hopefully you will have
caught a bunch of snails.

Most folks do preventive treatments of plants they put
in the pond, as many snails sneak in this way, very small or
as eggs. A weak solution of bleach will work, soak
the plant for 24 hours. Someone have a ratio of bleach
to water? Some folks use potassium permanganate
soaks but that stuff scares me!

k :-)