Cleaing hydor koralia powerhead

Make a vinegar/water solution and let it run in there for a day, then scrub off all the junk.
After that, run it in some clean water for a day before using.

Ordinary chlorine bleach works very well for cleaning aquarium equipment. You do have to rinse off the residue, and it is a good idea to use a soak with Prime in it as the last rinse. The hard part of cleaning a Koralia powerhead is taking it apart and putting it back together. To me that is much harder than for normal powerheads, but essential if you really want to clean it.

Bleach is by far the most accepted way to kill bacteria and sterilize things. Vinegar is good for cleaning alkaline water deposits but it does very little for killing bacteria. Vinegar is made by letting bacteria ferment apple juice and still has lots of bacteria in it when we pour it out of the jug.
Any worries about the chlorine in bleach are not well thought out. Chlorine is a gas by nature and will blow away as things dry. The reason you smell chlorine nears pools or spas is because it is coming out of the water and blowing away.

I dipped mine in a bunch of h202 once...I guess bleach makes more sense though but eh.

I probably go for the bleach as much because it is always here as much as any other reason. My wife always uses the cheaper non-scented anyway so it just makes one less item for me to store as we share the jug.
But then I also still have a stock of jeans with holes from water treatment work. We used to go out and pour gallons and gallons of bleach into wellheads to clear bacteria and I got pretty sloppy with it.
Bleach on your clothes is a bad deal but it is pretty safe if you pay attention to a few details.