Maintaining a pond with a small fountain in property

[Anil J.]

We got a SFH rental. It has a small pond (more like a pond+fountain) about 4'x6' or so; about 6 inches in depth. I just bought this property last year. Over the winter, with rain, the pond started developing a lot of algae and green stuff in the water. Now tenant is complaining about it.

Has anyone had any experience with dealing with it?

What are some inexpensive options to maintaining the pond? Should I get rid of the pond for rental purposes? (it's kind of nice looking, just might require some maintenance).

Can I just fill it with dirt or sand? (no drainage though...).

Thank you!