The Midi bale is perfect for ponds up to 3000 Gallons, while the Maxi bales will treat up to 9000. Simply place the bale in the water and the straw will do its work. If you have a persistent algae problem, use 2 bales per 3000 gallons of water.Algae problems in ponds can become a problem for the ecosystem if not treated. The TAP Barley straw bales are 100% natural making them easy on the life living within the pond.When the bale is introduced to the pond and becomes wet, a natural enzyme is released which helps to combat algae in a completely natural way. The end result is crystal clear water.The TAP barley bales have the additional benefit of added Lavender. Research has shown that the addition of lavender greatly increases the effectiveness of the straw.