[wooddood]

first off i am definately not as knowledgeable as alot of people here but heres my thoughts pista01.i would put the intake as far away fro the overflow as possible because your overflow is there to collect all the waste products from the tank.so the returns shoul be posisioned to create not only more water flow in the tank but to also direct the flow to the overflow so m ost of the waste is going to the overflow and into the sump to be purified.at least thats my line of thinking.as far as the return pump being in the 500 to 700gph range/with spray bars,i think i would up that because i think you should have at least a 10x turn over rate on your gph.also with the closed loop i would stay in the 700gph range on a 75gal tank,i think 1200 would be over kill.dont take this as the gospel though.lets see what else is recomended.hth.