Thanks for the help, I appreciate it. The right two bulkheads are plugged, and so is the left one. The only one that was being used is the furthermost on the left, and that pumped water back to the tank and split it right before it went up to hit both returns. I got the in and out figured out now, it's just the bio filtration I'm worried about now. Everything you said made sense in theory, and probably correct in practice too, but it seems weird how it is set up compared to others I have seen online now.
I think I am going to modify this one so it works better. Tell me what you think about this: The #4 area (furthermost right) I will have two drains coming in with filter socks attached. That's it for that section. Then I will seal the bottom off for that section with some type of divider. I have seen acrylic and glass, but where do you get these dividers? I can just silicone the divider in right? Then I will drill holes in the top of the wall between section 3 and 4 so the water flows into section 3 from the top. I can then have a filter pad on top of bio balls supported by egg crate shelf. Water will then flow under the divider that exists presently from section 2 to 3. I will have to add another divider from the bottom to around 8 inches from the top for water to climb up again and fall over that divider into section 2. I can have the same setup in section 2 with bio balls or ceramic rings right? More is better yeah? Then the water will flow under the existing divider between section 1 and 2. Just to the left of that divider before the water enters section 1, I can have some bio bags filled with carbon or more balls/rings. I can put my heaters in section 1 also.
Sound good? What would you do differently, if anything? Where do you get more egg crate stuff and divider material? Also, I hear you don't want your bio balls submerged. Is this right? What should my water level be in this thing? Directly under the bio balls, midway up, or totally submerged?