Float the net of Barley Straw in your pond. Ideally it should be tethered just below the surface, near the water outlet.
Use one net per 1000 gallons. (approximately). For smaller ponds of less than 500 gallons, cut a net in half, re-tie the ends and use one half at a time.
When the straw has almost fully decayed. put a fresh net into the pond and then two weeks later remove the old one.