Al algae turf scrubber (ATS) is a device that spreads water flow over a wide area with good surface traction, under lights, encouraging algae to grow. If you google Algae turf scrubber, you'll see all sorts of designs. TigerBarbs posted a link showing a cool design that fits in a small space, using a PVC pipe with a slit cut down the length. A sheet of stiff plastic mesh (craft store) is roughed up with sandpaper and inserted into this slit. End of the pipe is capped, forcing water to flow across the mesh. With lights shining on the mesh, algae will grow wild on it, sucking all the nutrients out of the water. Periodically, you just clean off about 75% of the mesh and let it grow back. Nice and fast nutrient export.
Another option would be to add some Macro Algae (AKA seaweed) to the tank.