I'm thinking you mentioned bleaching as a drastic thing that COULD be done, rather than what you do?
For me, my canisters are watched for reduced flow. Over time, I've found they do quite well on a more or less, two month "schedule". One big advantage to canisters is that the flow will let you know when they are getting full. HOB just bypass the water, canisters do not. As the flow slowly goes down, my need to clean goes up. At some point, it gets done. Better sooner but sometimes later. Sounds like that might fit your travels.
On the gunk coming out, I'm guessing there was maybe more work done around the tubing that maybe broke some of the grung inside loose? I often get that if I rearrange the tubes. Lots of minerals gather on the tube walls and breaks off. Does come out like a smokey cloud but it is still just stuff in the water, just out where I see it. It is reaborbed right away and goes back where I can't see it!