Do my snails need killing in my pond?

I have great pond, lesser pond, ramshorn, striped trapdoor, giant trapdoor, physa, MTS, nerite, apple and hooded snails. I have noticed less duckweed, less water hyacinth/lettuce, less crispa and several big clutches of snail eggs.

You have many species of snails. I assume that you added them on purpose. So, I'm wondering why you would then want to kill them? Snails do eat many plants.