I think a 404 would be adequate for a 75, but barely so, and a very nice complement to it would be a larger HOB
, like a Penguin 330 or Emperor 400. For larger tanks I like to have dual filtration, and a canister with a HOB
does the job very nicely.
As far as your bacterial colony (forgive me as I don't think I have read the previous post) if it is an established tank, putting a brand spanking new filter on it should not start a cycle at all. There should be tons of bacteria in the tank itself on all of the surfaces. I have never had a problem putting a new filter with 100% new media on an established tank. It does not hurt to transfer media to the new filter, certainly, but it is not required unless the tank is a relatively new setup.