Not the actual poop.
Those of us who keep fish buy filter media, where beneficial bacteria grows to help the fish.
Not the most expensive stuff in the world, but I love to save money. Over the years I've used these.

I walk my dogs, and I'm always cleaning up after them on trails and in the yard. These little black rolls hold the bags together, have ridges and holes. Perfect place for bacteria to grow.

I put them in these mesh bags and put them in the filters. When I want to start another tank; I just toss these into the filter of the tank itself to get it going.
Those of us who keep fish buy filter media, where beneficial bacteria grows to help the fish.
Not the most expensive stuff in the world, but I love to save money. Over the years I've used these.

I walk my dogs, and I'm always cleaning up after them on trails and in the yard. These little black rolls hold the bags together, have ridges and holes. Perfect place for bacteria to grow.

I put them in these mesh bags and put them in the filters. When I want to start another tank; I just toss these into the filter of the tank itself to get it going.