This filter might not meet the low cost requirement of most DIY projects but it does offer a needle-wheel/reactor option for CO2 users, for around $22. I have not tested the Fluval but the bubbles that come out of the Duetto filter act very much like water and most never make it to the waters surface.
I decided to post the modifications because they are both quick and effective. Well that and the possibility that someone's Marineland Duetto was sitting in a box of junk until a time when lemonade could be made out of their lemon.
Unfortunately, Marineland stopped making this filter and our source for lemons dried up. Time for an updated version.
Enter the Fluval nano filter. Placed under a pile of oak leaves for over two months it was still circulating water.
So, it's not a bad little filter and should be around for some time.
Seen in the following picture, the filter has a removable center partition for easier cleaning. This also makes it easy to reach when modifying the large opening on the far end.
So, to modify the fluvial follow the previous Duetto modifications. Next, a 2.5" by 1.25" piece of plexiglass is added to the removable partition, restricting the flow of CO2 entering the main chamber. It should fit snug - you shouldn't need glue.
