My 135 tank im buying has a gravel substrate i was wondering if i have to remove this in order to put my sand down or can i put my sand over top of it and not have to go through a huge cycle again because it currently has 2 damsels a clown and an angel in the tank and its my only saltwater tank. Also should i buy a skimmer because it has live rock and soon live sand either way i take the gravel out or not and the filter is an Emperor 400. Is this adequate enough for the live rock and sand and some inverts and those 4 fish until i buy a sump from my lfs? thanks justin