I have started the annual task of cleaning up the koi pond, first things first get the debris off the pond floor. These year I have noticed a huge amount of grey earwig like 'insects' an also tiny small silvery / grey looking squid (very slimy) - what are these guys - are they healthy residents in the pond?

The squid kind of reminds me of a rattail maggot. You
can enter that in google image and see if it matches up.

Earwig type may be damselfly nymphs. See if they
match up in google to your critters.

k :-)