Biological filtration using foam attached to the tank's side or bottom glass?

[Christian J]

Why not simply glue a large black filter sponge mat (about 1/2-1 inch thick) to the side glass of the aquarium? The aquarium's ordinary water movement should ensure nitrification.

Could this be an alternative to living rock in quarantine tanks, or to the biological filtration normally achieved with unsightly internal canister filters?

Or how about placing an even larger and thicker filter foam mat on the entire bottom glass of a display tank (hidden by a thin layer of sand)? Would you get denitrification if the foam material is dense enough? If so it sounds more practical than a deep sandbed to me: less weight, and easier to remove if it doesn't work. To prevent heavy rocks from sinking down into the foam you could place them on some kind of pedestals.

 

[jrp1588]

I imagine putting it on the glass would look terrible. I also don't think it's dense enough to form anaerobic areas necessary for denitrification.

 

[HumbleFish]

A (seeded) filter sponge works great for biological filtration in a temporary QT environment.

But I'm not so sure how well it would hold up after years of saltwater exposure. Me thinks the rock would fare better.

 

[alexander_ktn]

It might work but is probably not too efficient.
If the sponge is too coarse you will have very little surface compared to live rock and thus little denitrification (I assume it would get overgrown by algae and detritus would settle in it, so you'd definitely get anoxic zones, but with little surface). If the sponge is too fine I would think that the nitrogen released by the denitrification would stay trapped in the sponge thus reducing its effective surface over time as well.

What I do think is that such a sponge could be a great breeding ground for copepods etc.

In a qt tank I would rather use equipment that can easily be removed in case you need to medicate.