Your tank looks great. All your plumbing is great.
What size PVC is that 1/2, 3/4? unable to tell from picture. - Answered my own question on this one, helps to read your journal :-)
The output from your canister is that split line going to the manifold and one direct to the tank or do you have everything into the manifold? If that case does it not cause flow to be really low?
What type of CO2 reactor are you using?
The filter output goes directly to the bottom of the manifold. (BTW, flow starts at the bottom to minimize the possibility of trapping air in the manifold). I am sure it reduces flow some, but i tried to minimize the number of corners and also keep the PVC diameter large for sections that carry all the flow.
The main sections are 1" PVC. The key was finding the Tees that are 1" straight through, with a 1/2" section teeing off of it. This way if I want more total flow I can open up a ball valve (partially or completely) and send the water through 1" PVC the whole way. This also lets me replace or remove the reactor or heater pretty easily while everything is running.
I chose to glue almost everything, which I may regret, but at least it doesn't leak. The only things that are screwed on are the hose barbs. That way I can replace them with different sizes if i need to. Use lots of tephlon tape and the threads and they wont leak.
The problem with using threaded fittings everywhere is that things don't come out at the right angle. You can add a union, which i think allows you to rotate it, but that adds length, and as you can see, things are already pretty tight.
The CO2 reactor is the Ista Mix Max. They make two sizes, and I think I have the "medium" one. With adjustable flow through it its seems fine. My tank is very small for an FX5 though, so if you need to dissolve lots of CO2 you might want the larger one. To decide between this type and the inline atomizers, you need to choose sides in the "misting vs. dissolving" CO2 debate. I honestly have no idea which one plants like better. Some people say its better to dissolve CO2 completely (like the mix max), and some people say it's better to send the tiny CO2 bubbles into the tank.