LadyRene75

New turt mom and new to aquariums and all that goes with it ISO help! 75 gallon tank with fx4 filter, housing 1 RES 5-6 in shell length, 3 large gold fish and 2 rubies minnows. Plus have 1 large TopFin coral bubbler and green killing machine. What filter media should I be using and in what order? Do I need a prefilled on the intake. Water is good for 1 week post 50% water change then starts to turn color yellowish. TIA - Michelle