[trouble]

hi i am setting up a sump on a 72 gallon bow front. i am fish only right now but would like to set it up properly for corals in the future. i have 1x400 g/h and 1x800 g/h power head, based on the amount of flow those two power heads are giving me how many g/h return should my pump give me. should i still stay around the 20x tank volume or can i go a little less.