Question RE Bugs in the Water

I have an outdoor pond (about 250-300 gallons) in which I had four goldfish
that were suffering with columnaris (cotton wool disease). Whilst inspecting
them, I noticed that we had a number of young in the pond and took the
decision to move the adults into a tank and treat them separately until they
are well.

In hope of removing any parasites or imperfection in the water, I drained
the pond and cleaned out a lot of the gunk, catching the young as I did,
which are now in another tank (not with the adults) with a small filter pump
(from an old aquarium) on the tanks to keep the oxygene and cleanliness of
the water.

Whilst doing this we noticed some bugs that caused me a little concern:

(1) A bright red (like pillar-box red) worm like creature, about 5mm in
length that wiggles around very much like a normal earthworm would, but a
lot faster, though it doesn't actually seem to go anywhere.

(2) A clear blob! Shaped like an earthworm, about 2cm in length and
completly see-through. In fact, if we hadn't been collecting the young we'd
have never seen this.

If you know what the bugs are ... if they are harmful and if so, how to get
rid of them, I would appreciate it, along with any general tips on what I
might do to keep the fish healthy.

I check the water chemical levels on a regular basis and change about 15-20
gallons of water each week. We have a few toads and a couple of frogs that
visit ... I would assume that they would help kleep things clean and someone
recommended getting a couple of Tench.