More sump pics
Why did you go with a closed-loop system? I have one on my 400 and now I wish I hadn't mostly for esthetic reasons, but also because of it being a nightmare with maintenance.
Are the pvc elbows in the pictures all returns?
Do you have a drain in the floor anywhere near the tank? I would imagine you will get a lot of water on the floor maintaining this monster.
Are the return pumps pulling water from below the intake? Are they self priming?
How deep is the cistern?