We have algaecide that you can use to keep it under control. Stop in and grab the 16oz bottle of Clean Max, which should last more than a year. Scrub the outside of the fountain with a brush or #2 steel wool and then add the liquid algaecide.
There are chemicals you can buy. Try zamzows or a pond or aquarium store. If all else fails, Amazon.
You should try calling the store.
Thanks! Your answer is awaiting moderation.