I can't find anywhere where the specs are listed for the Aqua Ultraviolet about flow rates to get algae. The maximum flow rate will only be enough to kill bacteria; algae needs to go through a UV
at much slower flow. I'm not saying the Aqua is inadequate, simply that I can't find this information.
If you really want UV
I think you would do well with a Turbo Twist 12x 36W
You would assuredly hit both algae and bacteria with this unit.
you might even hit algae with the 18w version, with loss of gph
due to head room from the filter.
As a note the 36w version is a tank but I highly recommend it. It is easily 6" by 1.5ft. It hangs nicely on the top of the aquarium though.