flow rate in reactor

can any one tell me what the flow rate through a reactor should be i want to set up one with carbon plus seachem de-nitrate in and am not sure what the flow rate should be going thru the reactor i have googled it some have the flow just dripping one drip every second some seam to have it faster so acn any one plz put me straight thank you its a aqua medic reactor one inlet at the bottom one on the top its about 14 inches in lengh







plus what does gfo stand for