Well another reason I want to get another canister is that the HOB is really loud and without it my tank would be totally silent, seeing as i keep it in my bedroom. Fluval 305s are really not quite there when it comes to filtering 60 gallons and I always like to have two filters running so that when I clean one or if one has a problem I have one still on the tank. As for surface agitation being a help to plants because they need oxygen, correct me if im wrong here but plants produce oxygen during the daytime and co2 at night and I turn on an airpump at night. So im pretty sure surface agitaition would only be good at night.