Hi Faryle,

I've had a hard time finding someone with an expertise in the topic of fountains, so I will try to help you as best I can.

I can not tell what the black substance is on your fountain, based from your picture only. It could be a mold, mildew, bacteria or an algae of some sort. It could also be debris like dirt or soot. It is just not possible to know for sure from your picture.

You might try calling a fountain or pond dealer/supplier to speak with them about this to find out how they recommend cleaning it. According to a Pen State Extension publication, care and maintenance of a fountain should look like this: 

"Ideally, the water in your bird bath should be changed every day to prevent dirt and debris from accumulating. Changing the water daily in the summer also prevents mosquito larvae from hatching in your bird bath, which is a concern where the West Nile virus may be present. You should also scrub your bath with a brush, mild soap, and water every week to remove algae."

I would focus on getting the black substance removed and cleaned, and then maintain it as mentioned above to keep this substance from building up again.

Here is more information:

https://extension.psu.edu/water-for-wildlife-bird-baths-and-backyard-ponds

I hope this helps a bit,

Dawn

thanks for the response. Since then, I discovered a product called "Zep" that has bleach and other things in it and it is intended for outdoor use - to get rid of mold, mildew and algae on furniture, statuary, etc. I combined that with a wire bristle brush which I had been afraid would take the white paint off the fountain (it didn't!!!). So, it looks much better now. Didn't get every bit off, but it's a big improvement. I rinsed it a couple of times in case the cleaner wasn't good for birds.