Hey pool owners! How much pool shock do you need to kill algae? It all depends on the color of your water. - If you have light green water or teal green water, it’s a newer algae bloom. Use a double dose of shock to kill it. - If you have dark green water, you’ve got significant algae growth. Use a triple dose of shock. - If you have black green water, this is the hardest algae to kill. Use a quadruple dose of shock. One pound of shock treats 10,000 gallons of water. So if you have a 20,000-gall