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I feel silly, but I really have no idea.
If it's bio I'd like to put it in the expansion slot on my bio wheel 200.
Edit: It came out of an old filter unit that died.
That's what I'm leaning towards as well. The only thing throwing me off is it's more like a hardy mesh material. It's definitely not foam.
It came off some kind of Tetra unit, but I can't find a model number to look it up.