I have my sump (29g tall) set up very similar except I have no chamber 1 as you call it. Fuge is last section sourced by a T off the return with the black acrylic too. Been running that way since 2005. Until last year I always battled a slime type algae growing on top of chaeto. I attributed it to not enough flow through the fuge. If I increase flow, the overflow of that chamber into the return pump area caused too many bubbles. I tried putting in a powerhead, but the chaeto always clogged it within a day or so. Then I came across plastic mesh screen #7 size. I made a cylinder of it securing it using zip ties, then cut a disk of this material for the bottom and secured with the ties also. Now I had a cylinder just short of 17 in tall x 3 in dia and slid it down into the corner of the fuge, which is about 17 in deep. Put my powerhead (185gph) in the bottom of it and have it pushing the water straight up. The mesh is tight enough to keep the chaeto out, but the water is drawn from the bottom and inward up along the side of the cylinder. I now have great circulation (bottom to top) with gentle up-welling at the surface.
Since installing, the slime is gone and chaeto is super clean now and growing fantastic. Fuge has a Kessil H80 over it with the spectrum set to the 51% at 100% intensity set by my Apex.
Just something to consider if you have issues with undesirable algae in your fuge.