Harmful
Bleach and other chemicals can be hazardous to birds when used in a birdbath, according to Wisconsin veterinarians Foster and Smith. They recommend using a scrub brush to remove algae. If necessary, use a mild detergent and rinse the structure thoroughly after doing so. Add clean water after all residue has been removed.
Maintain
To keep algae or mineral deposits from forming in your birdbath, clean it out and add fresh water daily, if possible. You can also add to your unit a product designed to keep this water clear. Make sure it is non-toxic; do not use chemicals designed for pools or hot tubs.
Reasons
Keeping your birdbath clean can prevent the spread of disease. It can also keep it from becoming unsightly should feathers or bird droppings get into the water. You can also prevent harmful insects such as mosquitoes from using this area to breed. Having clean water for birds to bathe in will also attract more of these creatures to your yard.