Great information. I just wanted to add one thing.
Once you have the tank cycled you can get into trouble when cleaning your filters. Rinse your reusable filter media in tank water, not in tap water or worse yet soapy tap water. This way the bacteria that live in the filter media will not be killed off, reducing the capacity of the tanks nitrogen cycle. You will still have bacteria in the gravel, etc but a large percentage live in the filter which gets a steady flow of food and water.
Yes, that is very true
. And you never want to completely change all of the filter media all at once.
Although I've always disagreed with the part about tap water killing the bacteria. I haven't found any proof to back that statement up. In fact, I've always rinsed my filter media with tap water...with no issues. I doubt they'd be so sensitive that they'd all die off because of chlorine (which is what everyone tends to blame for the "die offs" that supposedly will happen).
I think that it's possible something else found in tap water might kill them though it's probably not something common.
Of course, you also have to keep in mind that not everyone's tank has the same beneficial bacteria. There are actually multiple species that are sometimes present. I bet some of them are hardier then others. I remember a study being done...I'll have to look for it. There was also an article in Tropical Fish Hobbyist...over the summer, I believe?
It was really interesting!
But what I'm getting at is that if these die-offs do occur they are probably rare and possibly caused by something else.