The sponge filter comes in a triangle form (like those sold by a company called Lee (no relation). They also come in round, tubular and other shapes. An Internet search for sponge filters should get a lot of hits. However, to start you off, try this link:
Sponge Filters at Big Al's Online
With regards to the quarantine of non fish -- the same QT can be used IF no copper or other meds were used to cure the fish. This would require special cleaning of the QT to make it ready again for invertebrates. Regarding invertebrate quarantine, you might get some more info from this article:
An Ounce of Prevention is Worth a Pound of Cure: A Quarantine Tank for Everything by Steven Pro - Reefkeeping.com
Sponge Filters at Big Al's Online
With regards to the quarantine of non fish -- the same QT can be used IF no copper or other meds were used to cure the fish. This would require special cleaning of the QT to make it ready again for invertebrates. Regarding invertebrate quarantine, you might get some more info from this article:
An Ounce of Prevention is Worth a Pound of Cure: A Quarantine Tank for Everything by Steven Pro - Reefkeeping.com