Exo Terra Moss Ball Clarity and Odour Control. The Exo Terra Moss Ball helps provide crystal clear water and reduce odors. Designed to resemble its natural counterpart, the Exo Terra Moss Ball contains a special absorption resin that helps reduce many of the compounds that encourage unsightly organic matter accumulation. By absorbing and trapping phosphate, nitrite and nitrate within its core, the Exo Terra Moss Ball helps to create ideal conditions for animals and plants and makes aqua-terrarium maintenance easy. Traps phosphate, nitrite and nitrate Easy and effective deodorizer Reduces organic matter accumulation Effective for up to 2 months Treats 30-60 liter (10-20 gal) terrariums.