Davy,
I thought you got a lot of good answers.
Ponding is part science, part art.
You are putting perimeters on a pond that don't
work in nature so you aren't always going to get
the results you want.

Your rain shower probably allowed a lot of nutients
from your yard (dirt, fertilizer?) to run into the pond.
A pond now out of balance.
ANY kind of plant will use up excess nutrients. But
it will take time.

k :-)