Acquire Snails (and Goldfish)

What happens here

The creator retrieves a small snail from one of the water tanks and explains its origin. He mentions that he found these snails on the side of a dock at a prominent lake in Virginia and thought to himself, 'I wonder what would happen if I put snails in my water tank?' This step involves the collection of pond or lake snails that are known to consume algae and detritus. The video also shows a goldfish in the tank, suggesting that goldfish can also be part of this biological cleaning system.

Goal: Obtain natural biological cleaners for the water tank.