Carefully tip the birdbath to empty standing water and debris. Have a bucket on hand if you don't want the mess in the garden.
Use a bucket of water or a spray from the hose to rinse the birdbath.
Next, you need to kill algae and mildew to keep the water clean when you refill it. So, mix together a half-gallon of water and a quarter of a cup of bleach and pour it carefully into the basin of the birdbath.
Cover the bath with a tarp or piece of cardboard while the mixture saturates the algae. You don't want any birds landing in your bleach mix.
After ten minutes or so, pull on some rubber gloves and use a scrubber brush to scour away any standing muck.
Then rinse the basin with hot water making sure that all of the bleach mixture has been rinsed away.
Fill the birdbath back up with cool, clean water and put a couple of pennies in the bottom. The copper from the pennies will attract the algae so that it doesn't adhere to the bath itself making it easier to clean in the future.
I hope these tips help you and birds enjoy this season! I'm Mrs. Fixit and it's just that simple.