Answer: Depending on the type of weed treated and the type of product used, the effects of the treatment can be seen as quickly as the same day or as long as 30 days out. A lot of the herbicides we use target the process of photosynthesis, making them safe for humans and animals. Without photosynthesis, a plant cannot receive energy. Without energy, the plants die. And once a plant has been treated and has died, Mother Nature then takes over and the plant begins to decompose. You’ll often experience an algae bloom at this time, as the algae and the bacteria in the pond feeds on this decomposing biomass.