I am setting up a 29 gal. salt. I have an emperor 400 from when it was freashwater and was going to use it again. After thinking for a bit, could i just get two power heads that moved enough water and then saved my 400 for another fresh water setup. I would hate to use the 400 just for circulation purposes. Also, how many GPH would i need to circulate for a 29 gal.