Stephen Bros Barley Straw 100g
Barley Straw is a great natural inhibitor of algal growth.
I would not recommend it for ponds that have big algal problems or blanket weed, just ponds that aren't in full sun light that need that extra boost.
Each bag will do a pond of approx 2 square metres
Takes 6 weeks to become active and lasts for between 8 - 10 weeks