Seeding a new sponge filter

[Furry]

Exactly. Flow is key. I'd also recommend adding a bit of fish food to the tank to keep the bacteria fed while the new filter establishes. Just don't overdo it, or you'll get an algae bloom.

[penny]

Yeah, and if you're impatient like me, you can always cheat and use a bit of substrate from an established tank. That stuff's packed with bacteria too.

[korali]

Just remember to test your water daily during the transition. Better safe than sorry, especially if you've got sensitive fish in there.

[freshbait]

And don't clean the new sponge for at least a month. Let that biofilm build up nice and thick. It's gross but necessary.