Hey, I own the Fluval U3 filter for my 50 gallon (36x18x18) tank. It's a good filter, I don't replace the carbon cartridges in it, well I don't use them I just have the sponges and the ceramic bio media in the middle. The U2 is smaller, so it should be fine in your tank. One thing that I just recently did that I really really really really think is a good idea is I put it sideways near the top of the water on the side of the tank. This opened up a lot of space near the bottom of the tank for them as well as creates a little platform that they can sit on, the pull on the grates on top isn't enough to hurt them and there's a few spots (on the u3 atleast) that don't have any grates and are just flat pieces of plastic they can hang out on. I use the bottom outflow, I originally planned to use the spray bar pointed up but it created a really strong current on the bottom of my tank, I had an incident where I put bloodworms in their dish and came back a few minutes later and they were literally everywhere. Had to spend a while cleaning it up but oh well lesson learned. I use the bottom outflow and on the U3 you can adjust the flow rate, idk if you can on the U2 but I think you can. It's a neat little filter, I wish there was more space to customize it, would like to be able to squeeze some purigen in there somewhere..
