Tiny worm things...

Hi.
Having moved house and adopted the established fish pond which had about
12 good sized fish + 2 small Tench. I have come across the following.

The previous owner buit his own filter using 3 water containers. The
first has lots of bits of offcut pipe, second stage is a simple
seperatoin type chamer, 3rd stage rises through a bed of gravel to the pond.

Anyway, in order to slow down the flow into the first stage rather than
water pumping straight out the overflow, I put half a dozen filter
brushes into the chamber. This worked fine, but now there are tiny
wiggly worms about 2" long and perhaps the thickness of a couple of
hairs. (red in colour)

Are they a sign of something going wrong, will they endanger the fish,
should I remove the brushes as they seem to thrive in the bristles.

Look forward to your comments.

Ta.
Pete