2 media chambers?

[salt01]

I have 2 phosban reactors and i have 1 gfo in it and was going to put carbon in the other. My question is I have 1 pump and would like to run both chambers one into the other. what order should i put them in the gfo into the carbon or carbon into gfo linking them in series.

 

[Northstar24]

I believe you'd want to run GFO -> Carbon

 

[salt01]

Also how full should i fill the carbon reactor? 1/2 or 3/4 or full?