brackish aquariums (esp with the fish you have chosen) are closer to freshwater than marine. don't stress about it too much, no special filtration is required. I have seen live rock in a brackish aquarium but i think it was very salty. try hardy plants that like hard, alkaline water (that will kill some plants, ie. swords, before the salt will) Java fern does really well. orange chromides come in brackish water (at least at HWFF), BB gobies usually come from fresh.