Vinegar is a non-toxic solution for killing algae. A mixture of three parts water and one part vinegar can be sprayed on the algae, resulting in removal of the unsightly green growth while leaving nearby soil safe for other plants.
Though usually effective when diluted with water, vinegar can be applied with full strength on stubborn areas. It is also effective at killing mold, weeds and other fungi. Chlorine is often used to kill algae, but applying it to some materials can bleach them. Chlorine also creates a toxic environment for other plants when it makes contact with the soil. Vinegar is acidic and achieves the same results as chlorine without the negative side effects.