Convict2161
Aquarium Advice Addict
With HOBs that is a tell tale sign you need to clean your media out. With canisters you will experience decreased flow when your media needs changed. Odor or water params going out of whack should not happen unless you let one run for a year straight with no maintenance.
To the OP, keep up on your routine maintenance and this shouldn't be an issue. I'm not saying that you're not doing routine work but maybe be a little more thorough in cleaning the pads.
My AC50 did it once, and that was when I left the country for a few weeks and it needed cleaned badly.
I agree 100% with this post. If you have a good routine you'll have little to no issues.