cycling, bacteria, filter media change

[Memnoch]

i'm thinking of changing my office tank waterfall filter to a smaller one, also to clean , replace my filter media of my canister filter...
worried that the bacteria will die if I change it, does the bacteria live in my substrate too? or predominantly in the filter

[richietay]

Use back the biological media from the old filter.

[|squee|]

It's said that bacteria is everywhere in the tank. Change the filter but use the old media.