Sorry.
Mine is a box as well, but I set it up skippy style. The water enters from the bottom and, circlulates. It then rises through furnace screening, scrubbers (in mesh bags), through the water hyacynths and out the weir and down to the pond.
Prior to the falls filter, the water is pumped out of the pond by a submerged pump located in a skimmer box ( mechanical filtration insides prior to water entering pump) out to the UV and then into the falls/ filter.
My string algae issue actually went away when I removed some scrubbers, leaving more room for hyacynth to take over. Amazing how crystal clear the pond became after that.
BR