Perfect for out-competing the deadly bad bacteria that causes Aeromonas Alley, Coldwater beneficial bacteria is a must for Fall & Spring to keep your koi healthy and safe. Most regular strands of beneficial bacteria are only good when the water temp is above 50-55 degrees. Use cold water beneficial bacteria when the water temps are below this to help keep the water clean, waste-free and safe from the dreaded aeromonas bad bacteria.