I wouldnt use bleach but vinegar instead. Vinegar breaks down coralline and any cemented critters and rinses clean. When I vlean my skimmer and poweheads I just run them in vinegar for an hour, wipe them then rinse and back in they go.
I used to use vinegar but it seems like it would never clean the soft stuff very easily. Even at a strong concentration that ended up softening the power cable on my return pump, it wouldn't clean everything up. Perhaps I need to try a different type.