What doesn't make sense is using the small piece of filter sock. Unless there was other bacteria on other parts of the tank (ie. not just the filter sock) to start with.
The filter sock piece gets colonized while hanging out in the DT sump for a week, then putting it in the HOB filter insert slot ensures good flow through the fabric for the bacteria on it to process ammonia.
The piece is only about 3” x 4” but the fabric surface area is huge.