If you’ve ever had a power outage, trusting that your filter(s) or pump(s) will restart once the power returns is important. You typically can’t control when the power returns but you can influence whether your filter equipment restarts. How? Keep the impeller and its housing clean. That means cleaning your filter or pump regularly. Some brands are better than others at restarting, even with some resistance (i.e, restarting with some gunk on the impeller or in the housing). However, the best way to ensure that you don’t have restart issues is to remove any buildup that has had time to accumulate (e.g., detritus).
Nothing is worse than coming home from a long day of work, only to find out your power went out for 10 minutes and your filters/pumps didn’t restart because they’re dirty. If you depend on powerheads or the outflow of your filters for water movement, then you’re depending on them to oxygenate your tank. In that instance, a non-restarting filter can be fatal to your fish long before the beneficial bacteria begin to die off. A ten minute interruption won’t kill your fish but several hours might, especially if your tank is heavily stocked. Your fish will suffocate well before ammonia or nitrites get too high.