I'm an inveterate tinkerer, so I can say yes sponge works as a bottom substrate, so does the filter media mats. As to blackworms. That I don't feed. The follow work. Slate over undergravel filter or sponge or matting over undergravel filter. Courser reticulated filter foam in the 30-45 ppm range rinse much more easily and thoroughly than 60-100 which eventually plug with fines or algae and don't hold up to a lot of squish and rinse.
Yep sponge as moss mat objects works great! Or moss wall. I tack moss to it with fishing line and an upholstery needle, then you don't see the stitching. Undergravel, a filtermat then sand prevents anaerobic build up and the mat keeps the sand from sifting through.
I use a small cannister filter over a powerhead or airstone powered undergravel because I can set it up reverse flow. The cannister pushes water under the sand or mat or sponge, and up very diffused into aquarium where the intake tube, with a sponge prefilter removes the wastes. Less settles, less clogs, less chance of bed failure.
If its a small quiet cannister, it makes practically no noise. Unlike power filters, airstones, powerheads.
Also consider a simple trimmed down high quality, closed cell Eva exercise mat. Food,water and chemically impervious they are simpler to use in aquaria than many foams. They come in puzzle tiles that fit together.Just avoid the cheap ones, one solid color all the way through, no paint or coloring on top.
I get mine used from closing gyms, yoga studios etc. Or buy new and check the msds first to be sure.
I'll stop now. I've been a tinker for wayyyy too long.
