Thanks! I love him so much. He has a distinctly Darcy personality. You got it right, I do have a Hydro I sponge filter.
The filter works great. I can feel the slight suction of water when my hand gets near it. It's a gentle suction that my fish doesn't mind. This isn't the most recent picture of my tank (it was taken weeks ago before the extra plants and the fish), but I think you can get a sense of the scale with the heater and height of the aquarium in this picture:
I almost wish I got the longer sponge. Was it Hydro II? I don't recall, but it was like a hot dog rather than a hamburger, if you get what I mean. I think the length would let me utilize the space in the aquarium more efficiently. Other than that, I believe the filter is doing its job. It creates just a small amount of current in the surface - seeing that Mr. Darcy hasn't built a nest, it may be a tad too strong for a bubble nest to exist, but that's fine with me.