To remove algae from a Keurig reservoir, start by shifting the coffee maker to an area where it is not exposed to direct sunlight. Then, empty the water tank and use baking soda to scrub the algae off the reservoir. You may also want to descale the Keurig to fully sanitize it. If the whole kitchen is exposed to the sun, use a black covering such as matte vinyl to shield the Keurig reservoir. Algae are photosynthetic and aquatic by nature. They thrive in environments where there is exposure to water and direct sunlight. Coffee maker reservoirs are usually made from clear plastic so they are prone to algae attacks if they are exposed to direct sunlight.