Okay, so the first section is 10 wide as it pours into the next section, with a 1" gap on each side of the center baffle, correct? And then it falls 2"? At 1400gph, that should be just fine. Especially since you have the same again after the refugium.
Since it has had time to slime coat and it is saltwater, I'm guessing you still have it falling too far in the return section, or you have a leak in your plumbing perhaps. The return section may be hard to get do, but I imagine it is virtually bubble free. Is the water being drawn from the bottom inch of water of the return section? Do you have a bulkhead with an elbow pointing down?