I agree with the other answer given. If you managed to shove another fine sponge inside the coarse sponge it defeats the purpose of the coarse sponge. You get a coarse sponge so it does not clog as often, reducing maintenance. Having them stuffed together increases maintenance. Having them stacked would allow the coarse sponge to hold more bacteria and you'd have crystal clear water from the fine sponge. Plus, if you didn't rinse out the fine sponge as often as you'd like the coarse sponge would help cover you.I recently found out the differences and benefits of fine and coarse sponge filters and was wondering if I could maybe combine it like put fine sponge inside the coarse and get both benefits?