Bio ball, but cube. Aquarium filtration.

thingiverse

Bio "ball" for aquarium filters, but a cube with rounded edges. Actually the general shape is not that important. What is important is the large surface area, and open structure, and the gyroid infill pattern bio balls can probably be made better than injection moulded bio balls. That in part because of the structured surface from the layer lines. The downloadable file has no gyroid pattern, its a plain cube. If you use a gyroid patterned stl cura won't be able to slice it with thin walls or to something easy to print. This cube with 30mm sides takes about 17 minutes on my ender 3 pro, at 30mm/s 0.28mm layer height, 0.6mm line with and 8% infill. If you want more dense pattern you can increase infill percentage.