" A rule of thumb is (change your hummingbird feeder water) every three days in the summer in LA because the sun and heat make them go bad fast. If the sugar water gets a milky haze, it means the feeder is slimy inside and the sugar water has gone sour. And if you see black spots on the glass that's fungus and then the feeder becomes a deathtrap. "

― Terry Masear , Fastest Things on Wings: Rescuing Hummingbirds in Hollywood