Algae, a photosynthetic organism most often found in water, can also trouble homeowners. It can grow on grass in wet climates, sprout on rooftops and exterior walls and can appear in water gardens and home hydroponic systems. Algaecides are available that are specially designed to clear up algae. Several household products will also kill algae but can have unintended consequences around your home.
Household spray disinfectants, like the ones you use to clean your kitchen, bathroom or toilet, kill algae. They contain surfactants, chemical agents that allow them to deeply penetrate the algae. Spray disinfectants have alkaloid properties, which is what can cause chemical burns if your skin is exposed to them in highly concentrated levels. The alkaloid properties also cause damage to algae. After the spray disinfectant penetrates the algae, it kills it, along with any living organism like grass that is nearby. Spray disinfectants are not labeled for use as algaecides.
Chlorine bleach in the 3 to 6 percent solution you use in your laundry room will kill algae. Bleach also contains surfactants, so it can penetrate algae. Bleach can burn your skin if you touch it; it also burns and kills algae. Bleach is not labeled as an algaecide. If you use it to kill algae growing on or near plants, the bleach could kill them. Using bleach to kill algae growing in water will kill aquatic plants, fish, frogs and toads. Killing algae growing on a wall or a roof with bleach can be problematic because the bleach could leech color from your roof tiles or the material on the side of your house, leaving an algae-free discolored blotch behind.
Hydrogen peroxide, used as a household disinfectant and cleaning agent, kills algae. Hydrogen peroxide does not differentiate between algae and other organic items like plant roots, so it must be used with care to avoid killing desired plants. Hydrogen peroxide can be used in hydroponics or water gardens to kill algae in the system before new plants are added to it. If algae reappears, small amounts of hydrogen peroxide will kill it for a short time, but the algae will soon return. Higher levels of hydrogen peroxide will be needed to kill the algae each time until the amounts you have to use become dangerous for other plants.