If you have this flow sensor,
http://shop.aquacomputer.de/product_info…roducts_id=2294
that uses the flow cable 53027 then it just connects to the flow port on the Aquaero, not the Aquabus.
The D5 connects to the Aquabus high port.
If you have other MPS devices then you can use a 4 pin splitter cable or just solder the cables together.