Plumbing TLF Reactors - Waterflow Together or Seperate?

[Ryan-b]

I use the setup on the right with mine. I run carbon first gfo 2nd, I get a decent tumble on the carbon, and a slower flow through the gfo. When I notice everything slowing down I usually know its time to change the carbon. I will also test the phosphate level coming out of the reactor to determine if it's time to change both.