So I admit, I’m a bit of sponge addict! I LOVE sponges because I think they’re extremely versatile and hugely utilitarian. Typically reserved for mechanical filtration in canisters, HOBs, and other mechanical filters, sponges are also widely used as bio-media for air driven filters. Every time I stop by my LFS, I make it a point to check out the sponge selection. I buy square sheet sponges, cylinder sponges, pond sponges, etc. I always have a need for the non-standard types. Because I’m a
JIC (just in case) hobbyist, I will regularly buy them in the event a new use presents itself.

Cylinder shaped sponges of various diameters and thickness. Photo courtesy of the author.
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Rectangular sponges of various sizes and thickness. Photo courtesy of the author.
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Circular and flat sponges. Photo courtesy of the author.
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Sheet sponge. Photo courtesy of the author.
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The photos above show some of the various sponges I keep on hand. These all vary in size, thickness, and density.
The cylinder sponges (upper left) are typically used to pre-filter intakes of canisters and HOBs. I even keep one on the intake in the corner overflow of my pre-drilled 75g.
The rectangular sponges (upper right) typically go in HOBs, but I sometimes find customized uses for them. The circular sponges (lower left) are for various canisters. The funky shaped black piece in that photo is what remains of a sheet sponge that I’ve cut up for various special projects. A full sheet sponge is shown in the lower right photo. This is actually pond sponge that comes in sheets 18″ x 12″ x 1″. These are very handy when you need something very specific. You just cut it to fit what you need.