I see a couple of possible issues.
What is holding the reactors up?
When the reactors are filled, i would not be comfortable with the stress on the plumbing due to the weight of the full reactors. Why not just get 2 male barb fittings and run a hose from your manifold to the reactors sitting on the bottom of your stand?
Second, your whole "S" designed return line looks like it is going to cause you to loose a fair amount of flow. If you decide to redo the reactors design you can fix your plumbing into a more linear design with a manifold, which should decrease the resistance and increase your flow.
Just my opinions... I consider myself decent with plumbing and could help when i pick up the other tank or i can text you pictures of mine to show you what i am talking about.
keep up the solid work!