creatures in the substrate - what are they?

Lauris

New Fish
May 6, 2009
4
0
0
Melbourne, Aus.
#1
Hi I'm a newbie, but have 4 tropical and one goldfish tank.
They are about 12 months old, so established and I'm noticing strange crawlies in the bottom of the bucket when I vacuum the substrate.
My local aquarium isnt sure what they are or if they are harmful.
Four bristlenose have died from the one tank, so they can't be good!
One looks like a pale pink leech, only about 5mm long, moves like a leech.
then there's a long bright red thread like worm.
then a tiny, white pinprick sized hopped, zooms around the bucket, lots of them. All of these get zapped with hot water.
I keep my water well balanced and changed about 25% every week.

then I found something like a pale grey spider, it was trying to clean off the scum on its feet, and walked around like a spider. Kinda cute and maybe not harmful, but he came from my silver dollar tank. If he's safe I'd like to put him back.
I cant seem to google any of these things. All the other fish are fabulous and breeding, just my bristlenose died. I was very attached to these little guys and they all had names, so quite distressing.
Anyone any got any more clues or knowledge than my local aquarium?
thanks,
Lauris